2008-02-04 00:25:47

by [email protected]

[permalink] [raw]
Subject: file locking patches

The following changes are available from the locks branch of the git
repository at:

git://linux-nfs.org/~bfields/linux.git locks

These are just three small file-locking-related patches, mostly cleanup.
All of them have been unchanged in -mm for a while.

--b.

J. Bruce Fields (1):
locks: clarify posix_locks_deadlock

Matthew Wilcox (1):
file locks: Use wait_event_interruptible_timeout()

Vitaliy Gusev (1):
pid-namespaces-vs-locks-interaction

fs/locks.c | 125 ++++++++++++++++++++++++++-------------------------
include/linux/fs.h | 1 +
2 files changed, 65 insertions(+), 61 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 8b8388e..49354b9 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -125,6 +125,7 @@
#include <linux/syscalls.h>
#include <linux/time.h>
#include <linux/rcupdate.h>
+#include <linux/pid_namespace.h>

#include <asm/semaphore.h>
#include <asm/uaccess.h>
@@ -185,6 +186,7 @@ void locks_init_lock(struct file_lock *fl)
fl->fl_fasync = NULL;
fl->fl_owner = NULL;
fl->fl_pid = 0;
+ fl->fl_nspid = NULL;
fl->fl_file = NULL;
fl->fl_flags = 0;
fl->fl_type = 0;
@@ -553,6 +555,8 @@ static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
{
list_add(&fl->fl_link, &file_lock_list);

+ fl->fl_nspid = get_pid(task_tgid(current));
+
/* insert into file's list */
fl->fl_next = *pos;
*pos = fl;
@@ -584,6 +588,11 @@ static void locks_delete_lock(struct file_lock **thisfl_p)
if (fl->fl_ops && fl->fl_ops->fl_remove)
fl->fl_ops->fl_remove(fl);

+ if (fl->fl_nspid) {
+ put_pid(fl->fl_nspid);
+ fl->fl_nspid = NULL;
+ }
+
locks_wake_up_blocks(fl);
locks_free_lock(fl);
}
@@ -634,33 +643,6 @@ static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *s
return (locks_conflict(caller_fl, sys_fl));
}

-static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
-{
- int result = 0;
- DECLARE_WAITQUEUE(wait, current);
-
- __set_current_state(TASK_INTERRUPTIBLE);
- add_wait_queue(fl_wait, &wait);
- if (timeout == 0)
- schedule();
- else
- result = schedule_timeout(timeout);
- if (signal_pending(current))
- result = -ERESTARTSYS;
- remove_wait_queue(fl_wait, &wait);
- __set_current_state(TASK_RUNNING);
- return result;
-}
-
-static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
-{
- int result;
- locks_insert_block(blocker, waiter);
- result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
- __locks_delete_block(waiter);
- return result;
-}
-
void
posix_test_lock(struct file *filp, struct file_lock *fl)
{
@@ -673,55 +655,67 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
if (posix_locks_conflict(fl, cfl))
break;
}
- if (cfl)
+ if (cfl) {
__locks_copy_lock(fl, cfl);
- else
+ if (cfl->fl_nspid)
+ fl->fl_pid = pid_nr_ns(cfl->fl_nspid,
+ task_active_pid_ns(current));
+ } else
fl->fl_type = F_UNLCK;
unlock_kernel();
return;
}
-
EXPORT_SYMBOL(posix_test_lock);

-/* This function tests for deadlock condition before putting a process to
- * sleep. The detection scheme is no longer recursive. Recursive was neat,
- * but dangerous - we risked stack corruption if the lock data was bad, or
- * if the recursion was too deep for any other reason.
+/*
+ * Deadlock detection:
+ *
+ * We attempt to detect deadlocks that are due purely to posix file
+ * locks.
*
- * We rely on the fact that a task can only be on one lock's wait queue
- * at a time. When we find blocked_task on a wait queue we can re-search
- * with blocked_task equal to that queue's owner, until either blocked_task
- * isn't found, or blocked_task is found on a queue owned by my_task.
+ * We assume that a task can be waiting for at most one lock at a time.
+ * So for any acquired lock, the process holding that lock may be
+ * waiting on at most one other lock. That lock in turns may be held by
+ * someone waiting for at most one other lock. Given a requested lock
+ * caller_fl which is about to wait for a conflicting lock block_fl, we
+ * follow this chain of waiters to ensure we are not about to create a
+ * cycle.
*
- * Note: the above assumption may not be true when handling lock requests
- * from a broken NFS client. But broken NFS clients have a lot more to
- * worry about than proper deadlock detection anyway... --okir
+ * Since we do this before we ever put a process to sleep on a lock, we
+ * are ensured that there is never a cycle; that is what guarantees that
+ * the while() loop in posix_locks_deadlock() eventually completes.
*
- * However, the failure of this assumption (also possible in the case of
- * multiple tasks sharing the same open file table) also means there's no
- * guarantee that the loop below will terminate. As a hack, we give up
- * after a few iterations.
+ * Note: the above assumption may not be true when handling lock
+ * requests from a broken NFS client. It may also fail in the presence
+ * of tasks (such as posix threads) sharing the same open file table.
+ *
+ * To handle those cases, we just bail out after a few iterations.
*/

#define MAX_DEADLK_ITERATIONS 10

+/* Find a lock that the owner of the given block_fl is blocking on. */
+static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
+{
+ struct file_lock *fl;
+
+ list_for_each_entry(fl, &blocked_list, fl_link) {
+ if (posix_same_owner(fl, block_fl))
+ return fl->fl_next;
+ }
+ return NULL;
+}
+
static int posix_locks_deadlock(struct file_lock *caller_fl,
struct file_lock *block_fl)
{
- struct file_lock *fl;
int i = 0;

-next_task:
- if (posix_same_owner(caller_fl, block_fl))
- return 1;
- list_for_each_entry(fl, &blocked_list, fl_link) {
- if (posix_same_owner(fl, block_fl)) {
- if (i++ > MAX_DEADLK_ITERATIONS)
- return 0;
- fl = fl->fl_next;
- block_fl = fl;
- goto next_task;
- }
+ while ((block_fl = what_owner_is_waiting_for(block_fl))) {
+ if (i++ > MAX_DEADLK_ITERATIONS)
+ return 0;
+ if (posix_same_owner(caller_fl, block_fl))
+ return 1;
}
return 0;
}
@@ -1256,7 +1250,10 @@ restart:
if (break_time == 0)
break_time++;
}
- error = locks_block_on_timeout(flock, new_fl, break_time);
+ locks_insert_block(flock, new_fl);
+ error = wait_event_interruptible_timeout(new_fl->fl_wait,
+ !new_fl->fl_next, break_time);
+ __locks_delete_block(new_fl);
if (error >= 0) {
if (error == 0)
time_out_leases(inode);
@@ -2084,6 +2081,12 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
int id, char *pfx)
{
struct inode *inode = NULL;
+ unsigned int fl_pid;
+
+ if (fl->fl_nspid)
+ fl_pid = pid_nr_ns(fl->fl_nspid, task_active_pid_ns(current));
+ else
+ fl_pid = fl->fl_pid;

if (fl->fl_file != NULL)
inode = fl->fl_file->f_path.dentry->d_inode;
@@ -2124,16 +2127,16 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
}
if (inode) {
#ifdef WE_CAN_BREAK_LSLK_NOW
- seq_printf(f, "%d %s:%ld ", fl->fl_pid,
+ seq_printf(f, "%d %s:%ld ", fl_pid,
inode->i_sb->s_id, inode->i_ino);
#else
/* userspace relies on this representation of dev_t ;-( */
- seq_printf(f, "%d %02x:%02x:%ld ", fl->fl_pid,
+ seq_printf(f, "%d %02x:%02x:%ld ", fl_pid,
MAJOR(inode->i_sb->s_dev),
MINOR(inode->i_sb->s_dev), inode->i_ino);
#endif
} else {
- seq_printf(f, "%d <none>:0 ", fl->fl_pid);
+ seq_printf(f, "%d <none>:0 ", fl_pid);
}
if (IS_POSIX(fl)) {
if (fl->fl_end == OFFSET_MAX)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a516b67..b7736ab 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -872,6 +872,7 @@ struct file_lock {
struct list_head fl_block; /* circular list of blocked processes */
fl_owner_t fl_owner;
unsigned int fl_pid;
+ struct pid *fl_nspid;
wait_queue_head_t fl_wait;
struct file *fl_file;
unsigned char fl_flags;