2021-06-10 11:17:04

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 0/8] ext4, jbd2: fix 3 issues about bdev_try_to_free_page()

This patchset fix a potential filesystem inconsistency problem and two
use-after-free problems about bdev_try_to_free_page().

Patch 1-4: Fix a potential filesystem inconsistency problem caused by
freeing buffers and doing umount concurrently, and also do
some cleanup.
Patch 5-8: Add a shrinker to release journal_head of checkpoint buffers
and remove the buggy bdev_try_to_free_page() at all.

Changes since v3:
- Patch 2: Fix one spelling mistake.
- Patch 3: Drop unnecessary 'result' check codes.
- Patch 5, declare static for jbd2_journal_shrink_[scan|count](),
and use percpu_counter_read_positive() to calculate the number of
shrinkable journal heads.
- Add 'Reviewed-by' tag from Jan besides the fifth patch.


Hi Jan,

I modify the fifth patch as Dave suggested, please give a look at this
patch again.

Thanks,
Yi.

------------------

Changes since v2:
- Fix some comments and spelling mistakes on patch 2 and 3.
- Give up the solution of add refcount on super_block and fix the
use-after-free issue in bdev_try_to_free_page(), switch to introduce
a shrinker to free checkpoint buffers' journal_head and remove the
whole callback at all.

Changes since v1:
- Do not use j_checkpoint_mutex to fix the filesystem inconsistency
problem, introduce a new mark instead.
- Fix superblock use-after-free issue in blkdev_releasepage().
- Avoid race between bdev_try_to_free_page() and ext4_put_super().


Zhang Yi (8):
jbd2: remove the out label in __jbd2_journal_remove_checkpoint()
jbd2: ensure abort the journal if detect IO error when writing
original buffer back
jbd2: don't abort the journal when freeing buffers
jbd2: remove redundant buffer io error checks
jbd2,ext4: add a shrinker to release checkpointed buffers
jbd2: simplify journal_clean_one_cp_list()
ext4: remove bdev_try_to_free_page() callback
fs: remove bdev_try_to_free_page callback

fs/block_dev.c | 15 ---
fs/ext4/super.c | 29 ++---
fs/jbd2/checkpoint.c | 206 +++++++++++++++++++++++++++++-------
fs/jbd2/journal.c | 101 ++++++++++++++++++
fs/jbd2/transaction.c | 17 ---
include/linux/fs.h | 1 -
include/linux/jbd2.h | 37 +++++++
include/trace/events/jbd2.h | 101 ++++++++++++++++++
8 files changed, 414 insertions(+), 93 deletions(-)

--
2.31.1


2021-06-10 11:17:05

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 3/8] jbd2: don't abort the journal when freeing buffers

Now that we can be sure the journal is aborted once a buffer has failed
to be written back to disk, we can remove the journal abort logic in
jbd2_journal_try_to_free_buffers() which was introduced in
commit c044f3d8360d ("jbd2: abort journal if free a async write error
metadata buffer"), because it may cost and propably is not safe.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/jbd2/transaction.c | 17 -----------------
1 file changed, 17 deletions(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e8fc45fd751f..8804e126805f 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -2123,7 +2123,6 @@ int jbd2_journal_try_to_free_buffers(journal_t *journal, struct page *page)
{
struct buffer_head *head;
struct buffer_head *bh;
- bool has_write_io_error = false;
int ret = 0;

J_ASSERT(PageLocked(page));
@@ -2148,26 +2147,10 @@ int jbd2_journal_try_to_free_buffers(journal_t *journal, struct page *page)
jbd2_journal_put_journal_head(jh);
if (buffer_jbd(bh))
goto busy;
-
- /*
- * If we free a metadata buffer which has been failed to
- * write out, the jbd2 checkpoint procedure will not detect
- * this failure and may lead to filesystem inconsistency
- * after cleanup journal tail.
- */
- if (buffer_write_io_error(bh)) {
- pr_err("JBD2: Error while async write back metadata bh %llu.",
- (unsigned long long)bh->b_blocknr);
- has_write_io_error = true;
- }
} while ((bh = bh->b_this_page) != head);

ret = try_to_free_buffers(page);
-
busy:
- if (has_write_io_error)
- jbd2_journal_abort(journal, -EIO);
-
return ret;
}

--
2.31.1

2021-06-10 11:17:06

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 2/8] jbd2: ensure abort the journal if detect IO error when writing original buffer back

Although we merged c044f3d8360 ("jbd2: abort journal if free a async
write error metadata buffer"), there is a race between
jbd2_journal_try_to_free_buffers() and jbd2_journal_destroy(), so the
jbd2_log_do_checkpoint() may still fail to detect the buffer write
io error flag which may lead to filesystem inconsistency.

jbd2_journal_try_to_free_buffers() ext4_put_super()
jbd2_journal_destroy()
__jbd2_journal_remove_checkpoint()
detect buffer write error jbd2_log_do_checkpoint()
jbd2_cleanup_journal_tail()
<--- lead to inconsistency
jbd2_journal_abort()

Fix this issue by introducing a new atomic flag which only have one
JBD2_CHECKPOINT_IO_ERROR bit now, and set it in
__jbd2_journal_remove_checkpoint() when freeing a checkpoint buffer
which has write_io_error flag. Then jbd2_journal_destroy() will detect
this mark and abort the journal to prevent updating log tail.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/jbd2/checkpoint.c | 12 ++++++++++++
fs/jbd2/journal.c | 14 ++++++++++++++
include/linux/jbd2.h | 11 +++++++++++
3 files changed, 37 insertions(+)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index bf5511d19ac5..d27c10f4502f 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -564,6 +564,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
struct transaction_chp_stats_s *stats;
transaction_t *transaction;
journal_t *journal;
+ struct buffer_head *bh = jh2bh(jh);

JBUFFER_TRACE(jh, "entry");

@@ -575,6 +576,17 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
journal = transaction->t_journal;

JBUFFER_TRACE(jh, "removing from transaction");
+
+ /*
+ * If we have failed to write the buffer out to disk, the filesystem
+ * may become inconsistent. We cannot abort the journal here since
+ * we hold j_list_lock and we have to be careful about races with
+ * jbd2_journal_destroy(). So mark the writeback IO error in the
+ * journal here and we abort the journal later from a better context.
+ */
+ if (buffer_write_io_error(bh))
+ set_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags);
+
__buffer_unlink(jh);
jh->b_cp_transaction = NULL;
jbd2_journal_put_journal_head(jh);
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2dc944442802..90146755941f 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1618,6 +1618,10 @@ int jbd2_journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,

if (is_journal_aborted(journal))
return -EIO;
+ if (test_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags)) {
+ jbd2_journal_abort(journal, -EIO);
+ return -EIO;
+ }

BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
jbd_debug(1, "JBD2: updating superblock (start %lu, seq %u)\n",
@@ -1995,6 +1999,16 @@ int jbd2_journal_destroy(journal_t *journal)
J_ASSERT(journal->j_checkpoint_transactions == NULL);
spin_unlock(&journal->j_list_lock);

+ /*
+ * OK, all checkpoint transactions have been checked, now check the
+ * write out io error flag and abort the journal if some buffer failed
+ * to write back to the original location, otherwise the filesystem
+ * may become inconsistent.
+ */
+ if (!is_journal_aborted(journal) &&
+ test_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags))
+ jbd2_journal_abort(journal, -EIO);
+
if (journal->j_sb_buffer) {
if (!is_journal_aborted(journal)) {
mutex_lock_io(&journal->j_checkpoint_mutex);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index db0e1920cb12..f9b5e657b8f3 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -779,6 +779,11 @@ struct journal_s
*/
unsigned long j_flags;

+ /**
+ * @j_atomic_flags: Atomic journaling state flags.
+ */
+ unsigned long j_atomic_flags;
+
/**
* @j_errno:
*
@@ -1371,6 +1376,12 @@ JBD2_FEATURE_INCOMPAT_FUNCS(fast_commit, FAST_COMMIT)
#define JBD2_FAST_COMMIT_ONGOING 0x100 /* Fast commit is ongoing */
#define JBD2_FULL_COMMIT_ONGOING 0x200 /* Full commit is ongoing */

+/*
+ * Journal atomic flag definitions
+ */
+#define JBD2_CHECKPOINT_IO_ERROR 0x001 /* Detect io error while writing
+ * buffer back to disk */
+
/*
* Function declarations for the journaling transaction and buffer
* management
--
2.31.1

2021-06-10 11:17:06

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 1/8] jbd2: remove the out label in __jbd2_journal_remove_checkpoint()

The 'out' lable just return the 'ret' value and seems not required, so
remove this label and switch to return appropriate value immediately.
This patch also do some minor cleanup, no logical change.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/jbd2/checkpoint.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 63b526d44886..bf5511d19ac5 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -564,13 +564,13 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
struct transaction_chp_stats_s *stats;
transaction_t *transaction;
journal_t *journal;
- int ret = 0;

JBUFFER_TRACE(jh, "entry");

- if ((transaction = jh->b_cp_transaction) == NULL) {
+ transaction = jh->b_cp_transaction;
+ if (!transaction) {
JBUFFER_TRACE(jh, "not on transaction");
- goto out;
+ return 0;
}
journal = transaction->t_journal;

@@ -579,9 +579,9 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
jh->b_cp_transaction = NULL;
jbd2_journal_put_journal_head(jh);

- if (transaction->t_checkpoint_list != NULL ||
- transaction->t_checkpoint_io_list != NULL)
- goto out;
+ /* Is this transaction empty? */
+ if (transaction->t_checkpoint_list || transaction->t_checkpoint_io_list)
+ return 0;

/*
* There is one special case to worry about: if we have just pulled the
@@ -593,10 +593,12 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
* See the comment at the end of jbd2_journal_commit_transaction().
*/
if (transaction->t_state != T_FINISHED)
- goto out;
+ return 0;

- /* OK, that was the last buffer for the transaction: we can now
- safely remove this transaction from the log */
+ /*
+ * OK, that was the last buffer for the transaction, we can now
+ * safely remove this transaction from the log.
+ */
stats = &transaction->t_chp_stats;
if (stats->cs_chp_time)
stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
@@ -606,9 +608,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)

__jbd2_journal_drop_transaction(journal, transaction);
jbd2_journal_free_transaction(transaction);
- ret = 1;
-out:
- return ret;
+ return 1;
}

/*
--
2.31.1

2021-06-10 11:17:11

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 7/8] ext4: remove bdev_try_to_free_page() callback

After we introduce a jbd2 shrinker to release checkpointed buffer's
journal head, we could free buffer without bdev_try_to_free_page()
under memory pressure. So this patch remove the whole
bdev_try_to_free_page() callback directly. It also remove many
use-after-free issues relate to it together.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/ext4/super.c | 21 ---------------------
1 file changed, 21 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 80064e566f56..cff882cf0847 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1442,26 +1442,6 @@ static int ext4_nfs_commit_metadata(struct inode *inode)
return ext4_write_inode(inode, &wbc);
}

-/*
- * Try to release metadata pages (indirect blocks, directories) which are
- * mapped via the block device. Since these pages could have journal heads
- * which would prevent try_to_free_buffers() from freeing them, we must use
- * jbd2 layer's try_to_free_buffers() function to release them.
- */
-static int bdev_try_to_free_page(struct super_block *sb, struct page *page,
- gfp_t wait)
-{
- journal_t *journal = EXT4_SB(sb)->s_journal;
-
- WARN_ON(PageChecked(page));
- if (!page_has_buffers(page))
- return 0;
- if (journal)
- return jbd2_journal_try_to_free_buffers(journal, page);
-
- return try_to_free_buffers(page);
-}
-
#ifdef CONFIG_FS_ENCRYPTION
static int ext4_get_context(struct inode *inode, void *ctx, size_t len)
{
@@ -1656,7 +1636,6 @@ static const struct super_operations ext4_sops = {
.quota_write = ext4_quota_write,
.get_dquots = ext4_get_dquots,
#endif
- .bdev_try_to_free_page = bdev_try_to_free_page,
};

static const struct export_operations ext4_export_ops = {
--
2.31.1

2021-06-10 11:17:17

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 5/8] jbd2,ext4: add a shrinker to release checkpointed buffers

Current metadata buffer release logic in bdev_try_to_free_page() have
a lot of use-after-free issues when umount filesystem concurrently, and
it is difficult to fix directly because ext4 is the only user of
s_op->bdev_try_to_free_page callback and we may have to add more special
refcount or lock that is only used by ext4 into the common vfs layer,
which is unacceptable.

One better solution is remove the bdev_try_to_free_page callback, but
the real problem is we cannot easily release journal_head on the
checkpointed buffer, so try_to_free_buffers() cannot release buffers and
page under memory pressure, which is more likely to trigger
out-of-memory. So we cannot remove the callback directly before we find
another way to release journal_head.

This patch introduce a shrinker to free journal_head on the checkpointed
transaction. After the journal_head got freed, try_to_free_buffers()
could free buffer properly.

Signed-off-by: Zhang Yi <[email protected]>
Suggested-by: Jan Kara <[email protected]>
---
fs/ext4/super.c | 8 ++
fs/jbd2/checkpoint.c | 147 ++++++++++++++++++++++++++++++++++++
fs/jbd2/journal.c | 87 +++++++++++++++++++++
include/linux/jbd2.h | 26 +++++++
include/trace/events/jbd2.h | 101 +++++++++++++++++++++++++
5 files changed, 369 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d29f6aa7d96e..80064e566f56 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1174,6 +1174,7 @@ static void ext4_put_super(struct super_block *sb)
ext4_unregister_sysfs(sb);

if (sbi->s_journal) {
+ jbd2_journal_unregister_shrinker(sbi->s_journal);
aborted = is_journal_aborted(sbi->s_journal);
err = jbd2_journal_destroy(sbi->s_journal);
sbi->s_journal = NULL;
@@ -5178,6 +5179,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
sbi->s_ea_block_cache = NULL;

if (sbi->s_journal) {
+ jbd2_journal_unregister_shrinker(sbi->s_journal);
jbd2_journal_destroy(sbi->s_journal);
sbi->s_journal = NULL;
}
@@ -5504,6 +5506,12 @@ static int ext4_load_journal(struct super_block *sb,
ext4_commit_super(sb);
}

+ err = jbd2_journal_register_shrinker(journal);
+ if (err) {
+ EXT4_SB(sb)->s_journal = NULL;
+ goto err_out;
+ }
+
return 0;

err_out:
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 75a4f622afaf..1abdae44a3d8 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -79,6 +79,18 @@ static inline void __buffer_relink_io(struct journal_head *jh)
transaction->t_checkpoint_io_list = jh;
}

+/*
+ * Check a checkpoint buffer could be release or not.
+ *
+ * Requires j_list_lock
+ */
+static inline bool __cp_buffer_busy(struct journal_head *jh)
+{
+ struct buffer_head *bh = jh2bh(jh);
+
+ return (jh->b_transaction || buffer_locked(bh) || buffer_dirty(bh));
+}
+
/*
* Try to release a checkpointed buffer from its transaction.
* Returns 1 if we released it and 2 if we also released the
@@ -458,6 +470,137 @@ static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
return 0;
}

+/*
+ * journal_shrink_one_cp_list
+ *
+ * Find 'nr_to_scan' written-back checkpoint buffers in the given list
+ * and try to release them. If the whole transaction is released, set
+ * the 'released' parameter. Return the number of released checkpointed
+ * buffers.
+ *
+ * Called with j_list_lock held.
+ */
+static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
+ unsigned long *nr_to_scan,
+ bool *released)
+{
+ struct journal_head *last_jh;
+ struct journal_head *next_jh = jh;
+ unsigned long nr_freed = 0;
+ int ret;
+
+ if (!jh || *nr_to_scan == 0)
+ return 0;
+
+ last_jh = jh->b_cpprev;
+ do {
+ jh = next_jh;
+ next_jh = jh->b_cpnext;
+
+ (*nr_to_scan)--;
+ if (__cp_buffer_busy(jh))
+ continue;
+
+ nr_freed++;
+ ret = __jbd2_journal_remove_checkpoint(jh);
+ if (ret) {
+ *released = true;
+ break;
+ }
+
+ if (need_resched())
+ break;
+ } while (jh != last_jh && *nr_to_scan);
+
+ return nr_freed;
+}
+
+/*
+ * jbd2_journal_shrink_checkpoint_list
+ *
+ * Find 'nr_to_scan' written-back checkpoint buffers in the journal
+ * and try to release them. Return the number of released checkpointed
+ * buffers.
+ *
+ * Called with j_list_lock held.
+ */
+unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
+ unsigned long *nr_to_scan)
+{
+ transaction_t *transaction, *last_transaction, *next_transaction;
+ bool released;
+ tid_t first_tid = 0, last_tid = 0, next_tid = 0;
+ tid_t tid = 0;
+ unsigned long nr_freed = 0;
+ unsigned long nr_scanned = *nr_to_scan;
+
+again:
+ spin_lock(&journal->j_list_lock);
+ if (!journal->j_checkpoint_transactions) {
+ spin_unlock(&journal->j_list_lock);
+ goto out;
+ }
+
+ /*
+ * Get next shrink transaction, resume previous scan or start
+ * over again. If some others do checkpoint and drop transaction
+ * from the checkpoint list, we ignore saved j_shrink_transaction
+ * and start over unconditionally.
+ */
+ if (journal->j_shrink_transaction)
+ transaction = journal->j_shrink_transaction;
+ else
+ transaction = journal->j_checkpoint_transactions;
+
+ if (!first_tid)
+ first_tid = transaction->t_tid;
+ last_transaction = journal->j_checkpoint_transactions->t_cpprev;
+ next_transaction = transaction;
+ last_tid = last_transaction->t_tid;
+ do {
+ transaction = next_transaction;
+ next_transaction = transaction->t_cpnext;
+ tid = transaction->t_tid;
+ released = false;
+
+ nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_list,
+ nr_to_scan, &released);
+ if (*nr_to_scan == 0)
+ break;
+ if (need_resched() || spin_needbreak(&journal->j_list_lock))
+ break;
+ if (released)
+ continue;
+
+ nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_io_list,
+ nr_to_scan, &released);
+ if (*nr_to_scan == 0)
+ break;
+ if (need_resched() || spin_needbreak(&journal->j_list_lock))
+ break;
+ } while (transaction != last_transaction);
+
+ if (transaction != last_transaction) {
+ journal->j_shrink_transaction = next_transaction;
+ next_tid = next_transaction->t_tid;
+ } else {
+ journal->j_shrink_transaction = NULL;
+ next_tid = 0;
+ }
+
+ spin_unlock(&journal->j_list_lock);
+ cond_resched();
+
+ if (*nr_to_scan && next_tid)
+ goto again;
+out:
+ nr_scanned -= *nr_to_scan;
+ trace_jbd2_shrink_checkpoint_list(journal, first_tid, tid, last_tid,
+ nr_freed, nr_scanned, next_tid);
+
+ return nr_freed;
+}
+
/*
* journal_clean_checkpoint_list
*
@@ -580,6 +723,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)

__buffer_unlink(jh);
jh->b_cp_transaction = NULL;
+ percpu_counter_dec(&journal->j_jh_shrink_count);
jbd2_journal_put_journal_head(jh);

/* Is this transaction empty? */
@@ -642,6 +786,7 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
jh->b_cpnext->b_cpprev = jh;
}
transaction->t_checkpoint_list = jh;
+ percpu_counter_inc(&transaction->t_journal->j_jh_shrink_count);
}

/*
@@ -657,6 +802,8 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
assert_spin_locked(&journal->j_list_lock);
+
+ journal->j_shrink_transaction = NULL;
if (transaction->t_cpnext) {
transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 90146755941f..3746bb4fc431 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1954,6 +1954,91 @@ int jbd2_journal_load(journal_t *journal)
return -EIO;
}

+/**
+ * jbd2_journal_shrink_scan()
+ *
+ * Scan the checkpointed buffer on the checkpoint list and release the
+ * journal_head.
+ */
+static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
+ struct shrink_control *sc)
+{
+ journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+ unsigned long nr_to_scan = sc->nr_to_scan;
+ unsigned long nr_shrunk;
+ unsigned long count;
+
+ count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
+ trace_jbd2_shrink_scan_enter(journal, sc->nr_to_scan, count);
+
+ nr_shrunk = jbd2_journal_shrink_checkpoint_list(journal, &nr_to_scan);
+
+ count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
+ trace_jbd2_shrink_scan_exit(journal, nr_to_scan, nr_shrunk, count);
+
+ return nr_shrunk;
+}
+
+/**
+ * jbd2_journal_shrink_count()
+ *
+ * Count the number of checkpoint buffers on the checkpoint list.
+ */
+static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
+ struct shrink_control *sc)
+{
+ journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+ unsigned long count;
+
+ count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
+ trace_jbd2_shrink_count(journal, sc->nr_to_scan, count);
+
+ return count;
+}
+
+/**
+ * jbd2_journal_register_shrinker()
+ * @journal: Journal to act on.
+ *
+ * Init a percpu counter to record the checkpointed buffers on the checkpoint
+ * list and register a shrinker to release their journal_head.
+ */
+int jbd2_journal_register_shrinker(journal_t *journal)
+{
+ int err;
+
+ journal->j_shrink_transaction = NULL;
+
+ err = percpu_counter_init(&journal->j_jh_shrink_count, 0, GFP_KERNEL);
+ if (err)
+ return err;
+
+ journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
+ journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
+ journal->j_shrinker.seeks = DEFAULT_SEEKS;
+ journal->j_shrinker.batch = journal->j_max_transaction_buffers;
+
+ err = register_shrinker(&journal->j_shrinker);
+ if (err) {
+ percpu_counter_destroy(&journal->j_jh_shrink_count);
+ return err;
+ }
+
+ return 0;
+}
+
+/**
+ * jbd2_journal_unregister_shrinker()
+ * @journal: Journal to act on.
+ *
+ * Unregister the checkpointed buffer shrinker and destroy the percpu counter.
+ */
+void jbd2_journal_unregister_shrinker(journal_t *journal)
+{
+ percpu_counter_destroy(&journal->j_jh_shrink_count);
+ unregister_shrinker(&journal->j_shrinker);
+}
+
/**
* jbd2_journal_destroy() - Release a journal_t structure.
* @journal: Journal to act on.
@@ -2026,6 +2111,8 @@ int jbd2_journal_destroy(journal_t *journal)
brelse(journal->j_sb_buffer);
}

+ jbd2_journal_unregister_shrinker(journal);
+
if (journal->j_proc_entry)
jbd2_stats_proc_exit(journal);
iput(journal->j_inode);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index f9b5e657b8f3..23578506215f 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -909,6 +909,29 @@ struct journal_s
*/
struct buffer_head *j_chkpt_bhs[JBD2_NR_BATCH];

+ /**
+ * @j_shrinker:
+ *
+ * Journal head shrinker, reclaim buffer's journal head which
+ * has been written back.
+ */
+ struct shrinker j_shrinker;
+
+ /**
+ * @j_jh_shrink_count:
+ *
+ * Number of journal buffers on the checkpoint list. [j_list_lock]
+ */
+ struct percpu_counter j_jh_shrink_count;
+
+ /**
+ * @j_shrink_transaction:
+ *
+ * Record next transaction will shrink on the checkpoint list.
+ * [j_list_lock]
+ */
+ transaction_t *j_shrink_transaction;
+
/**
* @j_head:
*
@@ -1418,6 +1441,7 @@ extern void jbd2_journal_commit_transaction(journal_t *);

/* Checkpoint list management */
void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy);
+unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal, unsigned long *nr_to_scan);
int __jbd2_journal_remove_checkpoint(struct journal_head *);
void jbd2_journal_destroy_checkpoint(journal_t *journal);
void __jbd2_journal_insert_checkpoint(struct journal_head *, transaction_t *);
@@ -1528,6 +1552,8 @@ extern int jbd2_journal_set_features
(journal_t *, unsigned long, unsigned long, unsigned long);
extern void jbd2_journal_clear_features
(journal_t *, unsigned long, unsigned long, unsigned long);
+extern int jbd2_journal_register_shrinker(journal_t *journal);
+extern void jbd2_journal_unregister_shrinker(journal_t *journal);
extern int jbd2_journal_load (journal_t *journal);
extern int jbd2_journal_destroy (journal_t *);
extern int jbd2_journal_recover (journal_t *journal);
diff --git a/include/trace/events/jbd2.h b/include/trace/events/jbd2.h
index d16a32867f3a..a4dfe005983d 100644
--- a/include/trace/events/jbd2.h
+++ b/include/trace/events/jbd2.h
@@ -394,6 +394,107 @@ TRACE_EVENT(jbd2_lock_buffer_stall,
__entry->stall_ms)
);

+DECLARE_EVENT_CLASS(jbd2_journal_shrink,
+
+ TP_PROTO(journal_t *journal, unsigned long nr_to_scan,
+ unsigned long count),
+
+ TP_ARGS(journal, nr_to_scan, count),
+
+ TP_STRUCT__entry(
+ __field(dev_t, dev)
+ __field(unsigned long, nr_to_scan)
+ __field(unsigned long, count)
+ ),
+
+ TP_fast_assign(
+ __entry->dev = journal->j_fs_dev->bd_dev;
+ __entry->nr_to_scan = nr_to_scan;
+ __entry->count = count;
+ ),
+
+ TP_printk("dev %d,%d nr_to_scan %lu count %lu",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->nr_to_scan, __entry->count)
+);
+
+DEFINE_EVENT(jbd2_journal_shrink, jbd2_shrink_count,
+
+ TP_PROTO(journal_t *journal, unsigned long nr_to_scan, unsigned long count),
+
+ TP_ARGS(journal, nr_to_scan, count)
+);
+
+DEFINE_EVENT(jbd2_journal_shrink, jbd2_shrink_scan_enter,
+
+ TP_PROTO(journal_t *journal, unsigned long nr_to_scan, unsigned long count),
+
+ TP_ARGS(journal, nr_to_scan, count)
+);
+
+TRACE_EVENT(jbd2_shrink_scan_exit,
+
+ TP_PROTO(journal_t *journal, unsigned long nr_to_scan,
+ unsigned long nr_shrunk, unsigned long count),
+
+ TP_ARGS(journal, nr_to_scan, nr_shrunk, count),
+
+ TP_STRUCT__entry(
+ __field(dev_t, dev)
+ __field(unsigned long, nr_to_scan)
+ __field(unsigned long, nr_shrunk)
+ __field(unsigned long, count)
+ ),
+
+ TP_fast_assign(
+ __entry->dev = journal->j_fs_dev->bd_dev;
+ __entry->nr_to_scan = nr_to_scan;
+ __entry->nr_shrunk = nr_shrunk;
+ __entry->count = count;
+ ),
+
+ TP_printk("dev %d,%d nr_to_scan %lu nr_shrunk %lu count %lu",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->nr_to_scan, __entry->nr_shrunk,
+ __entry->count)
+);
+
+TRACE_EVENT(jbd2_shrink_checkpoint_list,
+
+ TP_PROTO(journal_t *journal, tid_t first_tid, tid_t tid, tid_t last_tid,
+ unsigned long nr_freed, unsigned long nr_scanned,
+ tid_t next_tid),
+
+ TP_ARGS(journal, first_tid, tid, last_tid, nr_freed,
+ nr_scanned, next_tid),
+
+ TP_STRUCT__entry(
+ __field(dev_t, dev)
+ __field(tid_t, first_tid)
+ __field(tid_t, tid)
+ __field(tid_t, last_tid)
+ __field(unsigned long, nr_freed)
+ __field(unsigned long, nr_scanned)
+ __field(tid_t, next_tid)
+ ),
+
+ TP_fast_assign(
+ __entry->dev = journal->j_fs_dev->bd_dev;
+ __entry->first_tid = first_tid;
+ __entry->tid = tid;
+ __entry->last_tid = last_tid;
+ __entry->nr_freed = nr_freed;
+ __entry->nr_scanned = nr_scanned;
+ __entry->next_tid = next_tid;
+ ),
+
+ TP_printk("dev %d,%d shrink transaction %u-%u(%u) freed %lu "
+ "scanned %lu next transaction %u",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->first_tid, __entry->tid, __entry->last_tid,
+ __entry->nr_freed, __entry->nr_scanned, __entry->next_tid)
+);
+
#endif /* _TRACE_JBD2_H */

/* This part must be outside protection */
--
2.31.1

2021-06-10 11:17:23

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 8/8] fs: remove bdev_try_to_free_page callback

After remove the unique user of sop->bdev_try_to_free_page() callback,
we could remove the callback and the corresponding blkdev_releasepage()
at all.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/block_dev.c | 15 ---------------
include/linux/fs.h | 1 -
2 files changed, 16 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 6cc4d4cfe0c2..e215da6d49b4 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1733,20 +1733,6 @@ ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
}
EXPORT_SYMBOL_GPL(blkdev_read_iter);

-/*
- * Try to release a page associated with block device when the system
- * is under memory pressure.
- */
-static int blkdev_releasepage(struct page *page, gfp_t wait)
-{
- struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super;
-
- if (super && super->s_op->bdev_try_to_free_page)
- return super->s_op->bdev_try_to_free_page(super, page, wait);
-
- return try_to_free_buffers(page);
-}
-
static int blkdev_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
@@ -1760,7 +1746,6 @@ static const struct address_space_operations def_blk_aops = {
.write_begin = blkdev_write_begin,
.write_end = blkdev_write_end,
.writepages = blkdev_writepages,
- .releasepage = blkdev_releasepage,
.direct_IO = blkdev_direct_IO,
.migratepage = buffer_migrate_page_norefs,
.is_dirty_writeback = buffer_check_dirty_writeback,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3c88fdb9b2a..c3277b445f96 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2171,7 +2171,6 @@ struct super_operations {
ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
struct dquot **(*get_dquots)(struct inode *);
#endif
- int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
long (*nr_cached_objects)(struct super_block *,
struct shrink_control *);
long (*free_cached_objects)(struct super_block *,
--
2.31.1

2021-06-10 11:17:32

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 6/8] jbd2: simplify journal_clean_one_cp_list()

Now that __try_to_free_cp_buf() remove checkpointed buffer or transaction
when the buffer is not 'busy', which is only called by
journal_clean_one_cp_list(). This patch simplify this function by remove
__try_to_free_cp_buf() and invoke __cp_buffer_busy() directly.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/jbd2/checkpoint.c | 30 ++++--------------------------
1 file changed, 4 insertions(+), 26 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 1abdae44a3d8..51d1eb2ffeb9 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -91,25 +91,6 @@ static inline bool __cp_buffer_busy(struct journal_head *jh)
return (jh->b_transaction || buffer_locked(bh) || buffer_dirty(bh));
}

-/*
- * Try to release a checkpointed buffer from its transaction.
- * Returns 1 if we released it and 2 if we also released the
- * whole transaction.
- *
- * Requires j_list_lock
- */
-static int __try_to_free_cp_buf(struct journal_head *jh)
-{
- int ret = 0;
- struct buffer_head *bh = jh2bh(jh);
-
- if (!jh->b_transaction && !buffer_locked(bh) && !buffer_dirty(bh)) {
- JBUFFER_TRACE(jh, "remove from checkpoint list");
- ret = __jbd2_journal_remove_checkpoint(jh) + 1;
- }
- return ret;
-}
-
/*
* __jbd2_log_wait_for_space: wait until there is space in the journal.
*
@@ -440,7 +421,6 @@ static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
{
struct journal_head *last_jh;
struct journal_head *next_jh = jh;
- int ret;

if (!jh)
return 0;
@@ -449,13 +429,11 @@ static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
do {
jh = next_jh;
next_jh = jh->b_cpnext;
- if (!destroy)
- ret = __try_to_free_cp_buf(jh);
- else
- ret = __jbd2_journal_remove_checkpoint(jh) + 1;
- if (!ret)
+
+ if (!destroy && __cp_buffer_busy(jh))
return 0;
- if (ret == 2)
+
+ if (__jbd2_journal_remove_checkpoint(jh))
return 1;
/*
* This function only frees up some memory
--
2.31.1

2021-06-10 11:18:42

by Zhang Yi

[permalink] [raw]
Subject: [RFC PATCH v4 4/8] jbd2: remove redundant buffer io error checks

Now that __jbd2_journal_remove_checkpoint() can detect buffer io error
and mark journal checkpoint error, then we abort the journal later
before updating log tail to ensure the filesystem works consistently.
So we could remove other redundant buffer io error checkes.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
fs/jbd2/checkpoint.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index d27c10f4502f..75a4f622afaf 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -91,8 +91,7 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
int ret = 0;
struct buffer_head *bh = jh2bh(jh);

- if (jh->b_transaction == NULL && !buffer_locked(bh) &&
- !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
+ if (!jh->b_transaction && !buffer_locked(bh) && !buffer_dirty(bh)) {
JBUFFER_TRACE(jh, "remove from checkpoint list");
ret = __jbd2_journal_remove_checkpoint(jh) + 1;
}
@@ -228,7 +227,6 @@ int jbd2_log_do_checkpoint(journal_t *journal)
* OK, we need to start writing disk blocks. Take one transaction
* and write it.
*/
- result = 0;
spin_lock(&journal->j_list_lock);
if (!journal->j_checkpoint_transactions)
goto out;
@@ -295,8 +293,6 @@ int jbd2_log_do_checkpoint(journal_t *journal)
goto restart;
}
if (!buffer_dirty(bh)) {
- if (unlikely(buffer_write_io_error(bh)) && !result)
- result = -EIO;
BUFFER_TRACE(bh, "remove from checkpoint");
if (__jbd2_journal_remove_checkpoint(jh))
/* The transaction was released; we're done */
@@ -356,8 +352,6 @@ int jbd2_log_do_checkpoint(journal_t *journal)
spin_lock(&journal->j_list_lock);
goto restart2;
}
- if (unlikely(buffer_write_io_error(bh)) && !result)
- result = -EIO;

/*
* Now in whatever state the buffer currently is, we
@@ -369,10 +363,7 @@ int jbd2_log_do_checkpoint(journal_t *journal)
}
out:
spin_unlock(&journal->j_list_lock);
- if (result < 0)
- jbd2_journal_abort(journal, result);
- else
- result = jbd2_cleanup_journal_tail(journal);
+ result = jbd2_cleanup_journal_tail(journal);

return (result < 0) ? result : 0;
}
--
2.31.1

2021-06-10 16:15:29

by Jan Kara

[permalink] [raw]
Subject: Re: [RFC PATCH v4 5/8] jbd2,ext4: add a shrinker to release checkpointed buffers

On Thu 10-06-21 19:24:37, Zhang Yi wrote:
> Current metadata buffer release logic in bdev_try_to_free_page() have
> a lot of use-after-free issues when umount filesystem concurrently, and
> it is difficult to fix directly because ext4 is the only user of
> s_op->bdev_try_to_free_page callback and we may have to add more special
> refcount or lock that is only used by ext4 into the common vfs layer,
> which is unacceptable.
>
> One better solution is remove the bdev_try_to_free_page callback, but
> the real problem is we cannot easily release journal_head on the
> checkpointed buffer, so try_to_free_buffers() cannot release buffers and
> page under memory pressure, which is more likely to trigger
> out-of-memory. So we cannot remove the callback directly before we find
> another way to release journal_head.
>
> This patch introduce a shrinker to free journal_head on the checkpointed
> transaction. After the journal_head got freed, try_to_free_buffers()
> could free buffer properly.
>
> Signed-off-by: Zhang Yi <[email protected]>
> Suggested-by: Jan Kara <[email protected]>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <[email protected]>

Honza

> ---
> fs/ext4/super.c | 8 ++
> fs/jbd2/checkpoint.c | 147 ++++++++++++++++++++++++++++++++++++
> fs/jbd2/journal.c | 87 +++++++++++++++++++++
> include/linux/jbd2.h | 26 +++++++
> include/trace/events/jbd2.h | 101 +++++++++++++++++++++++++
> 5 files changed, 369 insertions(+)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d29f6aa7d96e..80064e566f56 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1174,6 +1174,7 @@ static void ext4_put_super(struct super_block *sb)
> ext4_unregister_sysfs(sb);
>
> if (sbi->s_journal) {
> + jbd2_journal_unregister_shrinker(sbi->s_journal);
> aborted = is_journal_aborted(sbi->s_journal);
> err = jbd2_journal_destroy(sbi->s_journal);
> sbi->s_journal = NULL;
> @@ -5178,6 +5179,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> sbi->s_ea_block_cache = NULL;
>
> if (sbi->s_journal) {
> + jbd2_journal_unregister_shrinker(sbi->s_journal);
> jbd2_journal_destroy(sbi->s_journal);
> sbi->s_journal = NULL;
> }
> @@ -5504,6 +5506,12 @@ static int ext4_load_journal(struct super_block *sb,
> ext4_commit_super(sb);
> }
>
> + err = jbd2_journal_register_shrinker(journal);
> + if (err) {
> + EXT4_SB(sb)->s_journal = NULL;
> + goto err_out;
> + }
> +
> return 0;
>
> err_out:
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 75a4f622afaf..1abdae44a3d8 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -79,6 +79,18 @@ static inline void __buffer_relink_io(struct journal_head *jh)
> transaction->t_checkpoint_io_list = jh;
> }
>
> +/*
> + * Check a checkpoint buffer could be release or not.
> + *
> + * Requires j_list_lock
> + */
> +static inline bool __cp_buffer_busy(struct journal_head *jh)
> +{
> + struct buffer_head *bh = jh2bh(jh);
> +
> + return (jh->b_transaction || buffer_locked(bh) || buffer_dirty(bh));
> +}
> +
> /*
> * Try to release a checkpointed buffer from its transaction.
> * Returns 1 if we released it and 2 if we also released the
> @@ -458,6 +470,137 @@ static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
> return 0;
> }
>
> +/*
> + * journal_shrink_one_cp_list
> + *
> + * Find 'nr_to_scan' written-back checkpoint buffers in the given list
> + * and try to release them. If the whole transaction is released, set
> + * the 'released' parameter. Return the number of released checkpointed
> + * buffers.
> + *
> + * Called with j_list_lock held.
> + */
> +static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
> + unsigned long *nr_to_scan,
> + bool *released)
> +{
> + struct journal_head *last_jh;
> + struct journal_head *next_jh = jh;
> + unsigned long nr_freed = 0;
> + int ret;
> +
> + if (!jh || *nr_to_scan == 0)
> + return 0;
> +
> + last_jh = jh->b_cpprev;
> + do {
> + jh = next_jh;
> + next_jh = jh->b_cpnext;
> +
> + (*nr_to_scan)--;
> + if (__cp_buffer_busy(jh))
> + continue;
> +
> + nr_freed++;
> + ret = __jbd2_journal_remove_checkpoint(jh);
> + if (ret) {
> + *released = true;
> + break;
> + }
> +
> + if (need_resched())
> + break;
> + } while (jh != last_jh && *nr_to_scan);
> +
> + return nr_freed;
> +}
> +
> +/*
> + * jbd2_journal_shrink_checkpoint_list
> + *
> + * Find 'nr_to_scan' written-back checkpoint buffers in the journal
> + * and try to release them. Return the number of released checkpointed
> + * buffers.
> + *
> + * Called with j_list_lock held.
> + */
> +unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
> + unsigned long *nr_to_scan)
> +{
> + transaction_t *transaction, *last_transaction, *next_transaction;
> + bool released;
> + tid_t first_tid = 0, last_tid = 0, next_tid = 0;
> + tid_t tid = 0;
> + unsigned long nr_freed = 0;
> + unsigned long nr_scanned = *nr_to_scan;
> +
> +again:
> + spin_lock(&journal->j_list_lock);
> + if (!journal->j_checkpoint_transactions) {
> + spin_unlock(&journal->j_list_lock);
> + goto out;
> + }
> +
> + /*
> + * Get next shrink transaction, resume previous scan or start
> + * over again. If some others do checkpoint and drop transaction
> + * from the checkpoint list, we ignore saved j_shrink_transaction
> + * and start over unconditionally.
> + */
> + if (journal->j_shrink_transaction)
> + transaction = journal->j_shrink_transaction;
> + else
> + transaction = journal->j_checkpoint_transactions;
> +
> + if (!first_tid)
> + first_tid = transaction->t_tid;
> + last_transaction = journal->j_checkpoint_transactions->t_cpprev;
> + next_transaction = transaction;
> + last_tid = last_transaction->t_tid;
> + do {
> + transaction = next_transaction;
> + next_transaction = transaction->t_cpnext;
> + tid = transaction->t_tid;
> + released = false;
> +
> + nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_list,
> + nr_to_scan, &released);
> + if (*nr_to_scan == 0)
> + break;
> + if (need_resched() || spin_needbreak(&journal->j_list_lock))
> + break;
> + if (released)
> + continue;
> +
> + nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_io_list,
> + nr_to_scan, &released);
> + if (*nr_to_scan == 0)
> + break;
> + if (need_resched() || spin_needbreak(&journal->j_list_lock))
> + break;
> + } while (transaction != last_transaction);
> +
> + if (transaction != last_transaction) {
> + journal->j_shrink_transaction = next_transaction;
> + next_tid = next_transaction->t_tid;
> + } else {
> + journal->j_shrink_transaction = NULL;
> + next_tid = 0;
> + }
> +
> + spin_unlock(&journal->j_list_lock);
> + cond_resched();
> +
> + if (*nr_to_scan && next_tid)
> + goto again;
> +out:
> + nr_scanned -= *nr_to_scan;
> + trace_jbd2_shrink_checkpoint_list(journal, first_tid, tid, last_tid,
> + nr_freed, nr_scanned, next_tid);
> +
> + return nr_freed;
> +}
> +
> /*
> * journal_clean_checkpoint_list
> *
> @@ -580,6 +723,7 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
>
> __buffer_unlink(jh);
> jh->b_cp_transaction = NULL;
> + percpu_counter_dec(&journal->j_jh_shrink_count);
> jbd2_journal_put_journal_head(jh);
>
> /* Is this transaction empty? */
> @@ -642,6 +786,7 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
> jh->b_cpnext->b_cpprev = jh;
> }
> transaction->t_checkpoint_list = jh;
> + percpu_counter_inc(&transaction->t_journal->j_jh_shrink_count);
> }
>
> /*
> @@ -657,6 +802,8 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
> void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
> {
> assert_spin_locked(&journal->j_list_lock);
> +
> + journal->j_shrink_transaction = NULL;
> if (transaction->t_cpnext) {
> transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
> transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 90146755941f..3746bb4fc431 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1954,6 +1954,91 @@ int jbd2_journal_load(journal_t *journal)
> return -EIO;
> }
>
> +/**
> + * jbd2_journal_shrink_scan()
> + *
> + * Scan the checkpointed buffer on the checkpoint list and release the
> + * journal_head.
> + */
> +static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
> + struct shrink_control *sc)
> +{
> + journal_t *journal = container_of(shrink, journal_t, j_shrinker);
> + unsigned long nr_to_scan = sc->nr_to_scan;
> + unsigned long nr_shrunk;
> + unsigned long count;
> +
> + count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
> + trace_jbd2_shrink_scan_enter(journal, sc->nr_to_scan, count);
> +
> + nr_shrunk = jbd2_journal_shrink_checkpoint_list(journal, &nr_to_scan);
> +
> + count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
> + trace_jbd2_shrink_scan_exit(journal, nr_to_scan, nr_shrunk, count);
> +
> + return nr_shrunk;
> +}
> +
> +/**
> + * jbd2_journal_shrink_count()
> + *
> + * Count the number of checkpoint buffers on the checkpoint list.
> + */
> +static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
> + struct shrink_control *sc)
> +{
> + journal_t *journal = container_of(shrink, journal_t, j_shrinker);
> + unsigned long count;
> +
> + count = percpu_counter_read_positive(&journal->j_jh_shrink_count);
> + trace_jbd2_shrink_count(journal, sc->nr_to_scan, count);
> +
> + return count;
> +}
> +
> +/**
> + * jbd2_journal_register_shrinker()
> + * @journal: Journal to act on.
> + *
> + * Init a percpu counter to record the checkpointed buffers on the checkpoint
> + * list and register a shrinker to release their journal_head.
> + */
> +int jbd2_journal_register_shrinker(journal_t *journal)
> +{
> + int err;
> +
> + journal->j_shrink_transaction = NULL;
> +
> + err = percpu_counter_init(&journal->j_jh_shrink_count, 0, GFP_KERNEL);
> + if (err)
> + return err;
> +
> + journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
> + journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
> + journal->j_shrinker.seeks = DEFAULT_SEEKS;
> + journal->j_shrinker.batch = journal->j_max_transaction_buffers;
> +
> + err = register_shrinker(&journal->j_shrinker);
> + if (err) {
> + percpu_counter_destroy(&journal->j_jh_shrink_count);
> + return err;
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * jbd2_journal_unregister_shrinker()
> + * @journal: Journal to act on.
> + *
> + * Unregister the checkpointed buffer shrinker and destroy the percpu counter.
> + */
> +void jbd2_journal_unregister_shrinker(journal_t *journal)
> +{
> + percpu_counter_destroy(&journal->j_jh_shrink_count);
> + unregister_shrinker(&journal->j_shrinker);
> +}
> +
> /**
> * jbd2_journal_destroy() - Release a journal_t structure.
> * @journal: Journal to act on.
> @@ -2026,6 +2111,8 @@ int jbd2_journal_destroy(journal_t *journal)
> brelse(journal->j_sb_buffer);
> }
>
> + jbd2_journal_unregister_shrinker(journal);
> +
> if (journal->j_proc_entry)
> jbd2_stats_proc_exit(journal);
> iput(journal->j_inode);
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index f9b5e657b8f3..23578506215f 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -909,6 +909,29 @@ struct journal_s
> */
> struct buffer_head *j_chkpt_bhs[JBD2_NR_BATCH];
>
> + /**
> + * @j_shrinker:
> + *
> + * Journal head shrinker, reclaim buffer's journal head which
> + * has been written back.
> + */
> + struct shrinker j_shrinker;
> +
> + /**
> + * @j_jh_shrink_count:
> + *
> + * Number of journal buffers on the checkpoint list. [j_list_lock]
> + */
> + struct percpu_counter j_jh_shrink_count;
> +
> + /**
> + * @j_shrink_transaction:
> + *
> + * Record next transaction will shrink on the checkpoint list.
> + * [j_list_lock]
> + */
> + transaction_t *j_shrink_transaction;
> +
> /**
> * @j_head:
> *
> @@ -1418,6 +1441,7 @@ extern void jbd2_journal_commit_transaction(journal_t *);
>
> /* Checkpoint list management */
> void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy);
> +unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal, unsigned long *nr_to_scan);
> int __jbd2_journal_remove_checkpoint(struct journal_head *);
> void jbd2_journal_destroy_checkpoint(journal_t *journal);
> void __jbd2_journal_insert_checkpoint(struct journal_head *, transaction_t *);
> @@ -1528,6 +1552,8 @@ extern int jbd2_journal_set_features
> (journal_t *, unsigned long, unsigned long, unsigned long);
> extern void jbd2_journal_clear_features
> (journal_t *, unsigned long, unsigned long, unsigned long);
> +extern int jbd2_journal_register_shrinker(journal_t *journal);
> +extern void jbd2_journal_unregister_shrinker(journal_t *journal);
> extern int jbd2_journal_load (journal_t *journal);
> extern int jbd2_journal_destroy (journal_t *);
> extern int jbd2_journal_recover (journal_t *journal);
> diff --git a/include/trace/events/jbd2.h b/include/trace/events/jbd2.h
> index d16a32867f3a..a4dfe005983d 100644
> --- a/include/trace/events/jbd2.h
> +++ b/include/trace/events/jbd2.h
> @@ -394,6 +394,107 @@ TRACE_EVENT(jbd2_lock_buffer_stall,
> __entry->stall_ms)
> );
>
> +DECLARE_EVENT_CLASS(jbd2_journal_shrink,
> +
> + TP_PROTO(journal_t *journal, unsigned long nr_to_scan,
> + unsigned long count),
> +
> + TP_ARGS(journal, nr_to_scan, count),
> +
> + TP_STRUCT__entry(
> + __field(dev_t, dev)
> + __field(unsigned long, nr_to_scan)
> + __field(unsigned long, count)
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = journal->j_fs_dev->bd_dev;
> + __entry->nr_to_scan = nr_to_scan;
> + __entry->count = count;
> + ),
> +
> + TP_printk("dev %d,%d nr_to_scan %lu count %lu",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __entry->nr_to_scan, __entry->count)
> +);
> +
> +DEFINE_EVENT(jbd2_journal_shrink, jbd2_shrink_count,
> +
> + TP_PROTO(journal_t *journal, unsigned long nr_to_scan, unsigned long count),
> +
> + TP_ARGS(journal, nr_to_scan, count)
> +);
> +
> +DEFINE_EVENT(jbd2_journal_shrink, jbd2_shrink_scan_enter,
> +
> + TP_PROTO(journal_t *journal, unsigned long nr_to_scan, unsigned long count),
> +
> + TP_ARGS(journal, nr_to_scan, count)
> +);
> +
> +TRACE_EVENT(jbd2_shrink_scan_exit,
> +
> + TP_PROTO(journal_t *journal, unsigned long nr_to_scan,
> + unsigned long nr_shrunk, unsigned long count),
> +
> + TP_ARGS(journal, nr_to_scan, nr_shrunk, count),
> +
> + TP_STRUCT__entry(
> + __field(dev_t, dev)
> + __field(unsigned long, nr_to_scan)
> + __field(unsigned long, nr_shrunk)
> + __field(unsigned long, count)
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = journal->j_fs_dev->bd_dev;
> + __entry->nr_to_scan = nr_to_scan;
> + __entry->nr_shrunk = nr_shrunk;
> + __entry->count = count;
> + ),
> +
> + TP_printk("dev %d,%d nr_to_scan %lu nr_shrunk %lu count %lu",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __entry->nr_to_scan, __entry->nr_shrunk,
> + __entry->count)
> +);
> +
> +TRACE_EVENT(jbd2_shrink_checkpoint_list,
> +
> + TP_PROTO(journal_t *journal, tid_t first_tid, tid_t tid, tid_t last_tid,
> + unsigned long nr_freed, unsigned long nr_scanned,
> + tid_t next_tid),
> +
> + TP_ARGS(journal, first_tid, tid, last_tid, nr_freed,
> + nr_scanned, next_tid),
> +
> + TP_STRUCT__entry(
> + __field(dev_t, dev)
> + __field(tid_t, first_tid)
> + __field(tid_t, tid)
> + __field(tid_t, last_tid)
> + __field(unsigned long, nr_freed)
> + __field(unsigned long, nr_scanned)
> + __field(tid_t, next_tid)
> + ),
> +
> + TP_fast_assign(
> + __entry->dev = journal->j_fs_dev->bd_dev;
> + __entry->first_tid = first_tid;
> + __entry->tid = tid;
> + __entry->last_tid = last_tid;
> + __entry->nr_freed = nr_freed;
> + __entry->nr_scanned = nr_scanned;
> + __entry->next_tid = next_tid;
> + ),
> +
> + TP_printk("dev %d,%d shrink transaction %u-%u(%u) freed %lu "
> + "scanned %lu next transaction %u",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __entry->first_tid, __entry->tid, __entry->last_tid,
> + __entry->nr_freed, __entry->nr_scanned, __entry->next_tid)
> +);
> +
> #endif /* _TRACE_JBD2_H */
>
> /* This part must be outside protection */
> --
> 2.31.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR