This fixes a hang seen in jbd2_journal_release_jbd_inode
on a lot of Power 6 systems running with ext4. When we get
in the hung state, all I/O to the disk in question gets blocked
where we stay indefinitely. Looking at the task list, I can see
we are stuck in jbd2_journal_release_jbd_inode waiting on a
wake up. I added some debug code to detect this scenario and
dump additional data if we were stuck in jbd2_journal_release_jbd_inode
for longer than 30 minutes. When it hit, I was able to see that
i_flags was 0, suggesting we missed the wake up.
This patch changes i_flags to be an unsigned long, uses bit operators
to access it, and adds barriers around the accesses. Prior to applying
this patch, we were regularly hitting this hang on numerous systems
in our test environment. After applying the patch, the hangs no longer
occur.
Signed-off-by: Brian King <[email protected]>
---
fs/jbd2/commit.c | 12 ++++++++----
fs/jbd2/journal.c | 4 +++-
include/linux/jbd2.h | 2 +-
3 files changed, 12 insertions(+), 6 deletions(-)
diff -puN include/linux/jbd2.h~jbd2_ji_commit_barrier_patch include/linux/jbd2.h
--- linux-2.6/include/linux/jbd2.h~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
+++ linux-2.6-bjking1/include/linux/jbd2.h 2010-08-30 08:45:04.000000000 -0500
@@ -395,7 +395,7 @@ struct jbd2_inode {
struct inode *i_vfs_inode;
/* Flags of inode [j_list_lock] */
- unsigned int i_flags;
+ unsigned long i_flags;
};
struct jbd2_revoke_table_s;
diff -puN fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch fs/jbd2/commit.c
--- linux-2.6/fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
+++ linux-2.6-bjking1/fs/jbd2/commit.c 2010-08-30 08:45:04.000000000 -0500
@@ -26,7 +26,9 @@
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
+#include <linux/bitops.h>
#include <trace/events/jbd2.h>
+#include <asm/system.h>
/*
* Default IO end handler for temporary BJ_IO buffer_heads.
@@ -236,7 +238,7 @@ static int journal_submit_data_buffers(j
spin_lock(&journal->j_list_lock);
list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
mapping = jinode->i_vfs_inode->i_mapping;
- jinode->i_flags |= JI_COMMIT_RUNNING;
+ set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
spin_unlock(&journal->j_list_lock);
/*
* submit the inode data buffers. We use writepage
@@ -251,7 +253,8 @@ static int journal_submit_data_buffers(j
spin_lock(&journal->j_list_lock);
J_ASSERT(jinode->i_transaction == commit_transaction);
commit_transaction->t_flushed_data_blocks = 1;
- jinode->i_flags &= ~JI_COMMIT_RUNNING;
+ clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
+ smp_mb__after_clear_bit();
wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING);
}
spin_unlock(&journal->j_list_lock);
@@ -272,7 +275,7 @@ static int journal_finish_inode_data_buf
/* For locking, see the comment in journal_submit_data_buffers() */
spin_lock(&journal->j_list_lock);
list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
- jinode->i_flags |= JI_COMMIT_RUNNING;
+ set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
spin_unlock(&journal->j_list_lock);
err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
if (err) {
@@ -288,7 +291,8 @@ static int journal_finish_inode_data_buf
ret = err;
}
spin_lock(&journal->j_list_lock);
- jinode->i_flags &= ~JI_COMMIT_RUNNING;
+ clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
+ smp_mb__after_clear_bit();
wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING);
}
diff -puN fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch fs/jbd2/journal.c
--- linux-2.6/fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
+++ linux-2.6-bjking1/fs/jbd2/journal.c 2010-08-31 08:58:24.000000000 -0500
@@ -42,12 +42,14 @@
#include <linux/log2.h>
#include <linux/vmalloc.h>
#include <linux/backing-dev.h>
+#include <linux/bitops.h>
#define CREATE_TRACE_POINTS
#include <trace/events/jbd2.h>
#include <asm/uaccess.h>
#include <asm/page.h>
+#include <asm/system.h>
EXPORT_SYMBOL(jbd2_journal_extend);
EXPORT_SYMBOL(jbd2_journal_stop);
@@ -2206,7 +2208,7 @@ void jbd2_journal_release_jbd_inode(jour
restart:
spin_lock(&journal->j_list_lock);
/* Is commit writing out inode - we have to wait */
- if (jinode->i_flags & JI_COMMIT_RUNNING) {
+ if (test_bit(__JI_COMMIT_RUNNING, &jinode->i_flags)) {
wait_queue_head_t *wq;
DEFINE_WAIT_BIT(wait, &jinode->i_flags, __JI_COMMIT_RUNNING);
wq = bit_waitqueue(&jinode->i_flags, __JI_COMMIT_RUNNING);
_
Added to the ext4 patch queue, thanks!!!
- Ted
On Tue, Aug 31, 2010 at 09:07:16AM -0500, Brian King wrote:
>
> This fixes a hang seen in jbd2_journal_release_jbd_inode
> on a lot of Power 6 systems running with ext4. When we get
> in the hung state, all I/O to the disk in question gets blocked
> where we stay indefinitely. Looking at the task list, I can see
> we are stuck in jbd2_journal_release_jbd_inode waiting on a
> wake up. I added some debug code to detect this scenario and
> dump additional data if we were stuck in jbd2_journal_release_jbd_inode
> for longer than 30 minutes. When it hit, I was able to see that
> i_flags was 0, suggesting we missed the wake up.
>
> This patch changes i_flags to be an unsigned long, uses bit operators
> to access it, and adds barriers around the accesses. Prior to applying
> this patch, we were regularly hitting this hang on numerous systems
> in our test environment. After applying the patch, the hangs no longer
> occur.
>
> Signed-off-by: Brian King <[email protected]>
> ---
>
> fs/jbd2/commit.c | 12 ++++++++----
> fs/jbd2/journal.c | 4 +++-
> include/linux/jbd2.h | 2 +-
> 3 files changed, 12 insertions(+), 6 deletions(-)
>
> diff -puN include/linux/jbd2.h~jbd2_ji_commit_barrier_patch include/linux/jbd2.h
> --- linux-2.6/include/linux/jbd2.h~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
> +++ linux-2.6-bjking1/include/linux/jbd2.h 2010-08-30 08:45:04.000000000 -0500
> @@ -395,7 +395,7 @@ struct jbd2_inode {
> struct inode *i_vfs_inode;
>
> /* Flags of inode [j_list_lock] */
> - unsigned int i_flags;
> + unsigned long i_flags;
> };
>
> struct jbd2_revoke_table_s;
> diff -puN fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch fs/jbd2/commit.c
> --- linux-2.6/fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
> +++ linux-2.6-bjking1/fs/jbd2/commit.c 2010-08-30 08:45:04.000000000 -0500
> @@ -26,7 +26,9 @@
> #include <linux/backing-dev.h>
> #include <linux/bio.h>
> #include <linux/blkdev.h>
> +#include <linux/bitops.h>
> #include <trace/events/jbd2.h>
> +#include <asm/system.h>
>
> /*
> * Default IO end handler for temporary BJ_IO buffer_heads.
> @@ -236,7 +238,7 @@ static int journal_submit_data_buffers(j
> spin_lock(&journal->j_list_lock);
> list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
> mapping = jinode->i_vfs_inode->i_mapping;
> - jinode->i_flags |= JI_COMMIT_RUNNING;
> + set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
> spin_unlock(&journal->j_list_lock);
> /*
> * submit the inode data buffers. We use writepage
> @@ -251,7 +253,8 @@ static int journal_submit_data_buffers(j
> spin_lock(&journal->j_list_lock);
> J_ASSERT(jinode->i_transaction == commit_transaction);
> commit_transaction->t_flushed_data_blocks = 1;
> - jinode->i_flags &= ~JI_COMMIT_RUNNING;
> + clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
> + smp_mb__after_clear_bit();
> wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING);
> }
> spin_unlock(&journal->j_list_lock);
> @@ -272,7 +275,7 @@ static int journal_finish_inode_data_buf
> /* For locking, see the comment in journal_submit_data_buffers() */
> spin_lock(&journal->j_list_lock);
> list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) {
> - jinode->i_flags |= JI_COMMIT_RUNNING;
> + set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
> spin_unlock(&journal->j_list_lock);
> err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
> if (err) {
> @@ -288,7 +291,8 @@ static int journal_finish_inode_data_buf
> ret = err;
> }
> spin_lock(&journal->j_list_lock);
> - jinode->i_flags &= ~JI_COMMIT_RUNNING;
> + clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags);
> + smp_mb__after_clear_bit();
> wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING);
> }
>
> diff -puN fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch fs/jbd2/journal.c
> --- linux-2.6/fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch 2010-08-30 08:45:04.000000000 -0500
> +++ linux-2.6-bjking1/fs/jbd2/journal.c 2010-08-31 08:58:24.000000000 -0500
> @@ -42,12 +42,14 @@
> #include <linux/log2.h>
> #include <linux/vmalloc.h>
> #include <linux/backing-dev.h>
> +#include <linux/bitops.h>
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/jbd2.h>
>
> #include <asm/uaccess.h>
> #include <asm/page.h>
> +#include <asm/system.h>
>
> EXPORT_SYMBOL(jbd2_journal_extend);
> EXPORT_SYMBOL(jbd2_journal_stop);
> @@ -2206,7 +2208,7 @@ void jbd2_journal_release_jbd_inode(jour
> restart:
> spin_lock(&journal->j_list_lock);
> /* Is commit writing out inode - we have to wait */
> - if (jinode->i_flags & JI_COMMIT_RUNNING) {
> + if (test_bit(__JI_COMMIT_RUNNING, &jinode->i_flags)) {
> wait_queue_head_t *wq;
> DEFINE_WAIT_BIT(wait, &jinode->i_flags, __JI_COMMIT_RUNNING);
> wq = bit_waitqueue(&jinode->i_flags, __JI_COMMIT_RUNNING);
> _