On Wed, 28 Mar 2012 17:36:17 +0400
Pavel Shilovsky <piastry@xxxxxxxxxxx> wrote:
> We can deadlock if we have a write oplock and two processes
> use the same file handle. In this case the first process can't
> unlock its lock if the second process blocked on the lock in the
> same time.
>
> Fix it by using posix_lock_file rather than posix_lock_file_wait
> under cinode->lock_mutex. If we request a blocking lock and
> posix_lock_file indicates that there is another lock that prevents
> us, wait untill that lock is released and restart our call.
>
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Pavel Shilovsky <piastry@xxxxxxxxxxx>
> ---
> fs/cifs/file.c | 10 +++++++++-
> fs/locks.c | 3 ++-
> include/linux/fs.h | 5 +++++
> 3 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 460d87b..fae765d 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -835,13 +835,21 @@ cifs_posix_lock_set(struct file *file, struct file_lock *flock)
> if ((flock->fl_flags & FL_POSIX) == 0)
> return rc;
>
> +try_again:
> mutex_lock(&cinode->lock_mutex);
> if (!cinode->can_cache_brlcks) {
> mutex_unlock(&cinode->lock_mutex);
> return rc;
> }
> - rc = posix_lock_file_wait(file, flock);
> +
> + rc = posix_lock_file(file, flock, NULL);
> mutex_unlock(&cinode->lock_mutex);
> + if (rc == FILE_LOCK_DEFERRED) {
> + rc = wait_event_interruptible(flock->fl_wait, !flock->fl_next);
> + if (!rc)
> + goto try_again;
> + locks_delete_block(flock);
> + }
> return rc;
> }
>
> diff --git a/fs/locks.c b/fs/locks.c
> index 637694b..0d68f1f 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -510,12 +510,13 @@ static void __locks_delete_block(struct file_lock *waiter)
>
> /*
> */
> -static void locks_delete_block(struct file_lock *waiter)
> +void locks_delete_block(struct file_lock *waiter)
> {
> lock_flocks();
> __locks_delete_block(waiter);
> unlock_flocks();
> }
> +EXPORT_SYMBOL(locks_delete_block);
>
Since this now touches basic VFS layer code, you should also cc
linux-fsdevel and probably LKML.
> /* Insert waiter into blocker's block list.
> * We use a circular list so that processes can be easily woken up in
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index fa63f1b..d8fd8df 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1211,6 +1211,7 @@ extern int vfs_setlease(struct file *, long, struct file_lock **);
> extern int lease_modify(struct file_lock **, int);
> extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
> extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
> +extern void locks_delete_block(struct file_lock *waiter);
> extern void lock_flocks(void);
> extern void unlock_flocks(void);
> #else /* !CONFIG_FILE_LOCKING */
> @@ -1355,6 +1356,10 @@ static inline int lock_may_write(struct inode *inode, loff_t start,
> return 1;
> }
>
> +static inline void locks_delete_block(struct file_lock *waiter)
> +{
> +}
> +
> static inline void lock_flocks(void)
> {
> }
Well, I'm still not fond of this code in general, but it seems to fix a
real-world problem, so...
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
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