Hi Ryan,
On 11/20/2015 04:23 PM, Ryan Ding wrote:
> In the current implementation of unaligned aio+dio, lock order behave as
> follow:
>
> in user process context:
> -> call io_submit()
> -> get i_mutex
> <== window1
> -> get ip_unaligned_aio
> -> submit direct io to block device
> -> release i_mutex
> -> io_submit() return
>
> in dio work queue context(the work queue is created in __blockdev_direct_IO):
> -> release ip_unaligned_aio
> <== window2
> -> get i_mutex
> -> clear unwritten flag & change i_size
> -> release i_mutex
>
> There is a limitation to the thread number of dio work queue. 256 at default.
> If all 256 thread are in the above 'window2' stage, and there is a user
> process
> in the 'window1' stage, the system will became deadlock. Since the user
> process
> hold i_mutex to wait ip_unaligned_aio lock, while there is a direct bio hold
> ip_unaligned_aio mutex who is waiting for a dio work queue thread to be
> schedule. But all the dio work queue thread is waiting for i_mutex lock in
> 'window2'.
>
> This case only happened in a test which send a large number(more than 256) of
> aio at one io_submit() call.
>
> My design is to remove ip_unaligned_aio lock. Change it to a sync io instead.
> Just like ip_unaligned_aio lock, serialize the unaligned aio dio.
>
> Signed-off-by: Ryan Ding <ryan.d...@oracle.com>
> ---
> fs/ocfs2/aops.c | 6 ------
> fs/ocfs2/aops.h | 7 -------
> fs/ocfs2/file.c | 27 +++++++++------------------
> fs/ocfs2/inode.h | 3 ---
> fs/ocfs2/super.c | 1 -
> 5 files changed, 9 insertions(+), 35 deletions(-)
>
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index 4bb9921..cc604a2 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -2388,12 +2388,6 @@ static void ocfs2_dio_end_io(struct kiocb *iocb,
> /* this io's submitter should not have unlocked this before we could */
> BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));
>
> - if (ocfs2_iocb_is_unaligned_aio(iocb)) {
> - ocfs2_iocb_clear_unaligned_aio(iocb);
> -
> - mutex_unlock(&OCFS2_I(inode)->ip_unaligned_aio);
> - }
> -
> if (private)
> ocfs2_dio_end_io_write(inode, private, offset, bytes);
>
> diff --git a/fs/ocfs2/aops.h b/fs/ocfs2/aops.h
> index d06b80f..7fc1189 100644
> --- a/fs/ocfs2/aops.h
> +++ b/fs/ocfs2/aops.h
> @@ -93,11 +93,4 @@ enum ocfs2_iocb_lock_bits {
> #define ocfs2_iocb_rw_locked_level(iocb) \
> test_bit(OCFS2_IOCB_RW_LOCK_LEVEL, (unsigned long *)&iocb->private)
>
> -#define ocfs2_iocb_set_unaligned_aio(iocb) \
> - set_bit(OCFS2_IOCB_UNALIGNED_IO, (unsigned long *)&iocb->private)
> -#define ocfs2_iocb_clear_unaligned_aio(iocb) \
> - clear_bit(OCFS2_IOCB_UNALIGNED_IO, (unsigned long *)&iocb->private)
> -#define ocfs2_iocb_is_unaligned_aio(iocb) \
> - test_bit(OCFS2_IOCB_UNALIGNED_IO, (unsigned long *)&iocb->private)
> -
OCFS2_IOCB_UNALIGNED_IO is useless now. Please remove its definition.
Other looks good.
Reviewed-by: Junxiao Bi <junxiao...@oracle.com>
> #endif /* OCFS2_FILE_H */
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index 05346fb..6ab91cd 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2170,7 +2170,7 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
> struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
> int full_coherency = !(osb->s_mount_opt &
> OCFS2_MOUNT_COHERENCY_BUFFERED);
> - int unaligned_dio = 0;
> + void *saved_ki_complete = NULL;
> int append_write = ((iocb->ki_pos + count) >=
> i_size_read(inode) ? 1 : 0);
>
> @@ -2233,17 +2233,12 @@ static ssize_t ocfs2_file_write_iter(struct kiocb
> *iocb,
> goto out;
> }
>
> - if (direct_io && !is_sync_kiocb(iocb))
> - unaligned_dio = ocfs2_is_io_unaligned(inode, count,
> iocb->ki_pos);
> -
> - if (unaligned_dio) {
> + if (direct_io && !is_sync_kiocb(iocb) &&
> + ocfs2_is_io_unaligned(inode, count, iocb->ki_pos)) {
> /*
> - * Wait on previous unaligned aio to complete before
> - * proceeding.
> + * Make it a sync io if it's an unaligned aio.
> */
> - mutex_lock(&OCFS2_I(inode)->ip_unaligned_aio);
> - /* Mark the iocb as needing an unlock in ocfs2_dio_end_io */
> - ocfs2_iocb_set_unaligned_aio(iocb);
> + saved_ki_complete = xchg(&iocb->ki_complete, NULL);
> }
>
> /* communicate with ocfs2_dio_end_io */
> @@ -2264,11 +2259,10 @@ static ssize_t ocfs2_file_write_iter(struct kiocb
> *iocb,
> */
> if ((written == -EIOCBQUEUED) || (!ocfs2_iocb_is_rw_locked(iocb))) {
> rw_level = -1;
> - unaligned_dio = 0;
> }
>
> if (unlikely(written <= 0))
> - goto no_sync;
> + goto out;
>
> if (((file->f_flags & O_DSYNC) && !direct_io) ||
> IS_SYNC(inode)) {
> @@ -2290,13 +2284,10 @@ static ssize_t ocfs2_file_write_iter(struct kiocb
> *iocb,
> iocb->ki_pos - 1);
> }
>
> -no_sync:
> - if (unaligned_dio && ocfs2_iocb_is_unaligned_aio(iocb)) {
> - ocfs2_iocb_clear_unaligned_aio(iocb);
> - mutex_unlock(&OCFS2_I(inode)->ip_unaligned_aio);
> - }
> -
> out:
> + if (saved_ki_complete)
> + xchg(&iocb->ki_complete, saved_ki_complete);
> +
> if (rw_level != -1)
> ocfs2_rw_unlock(inode, rw_level);
>
> diff --git a/fs/ocfs2/inode.h b/fs/ocfs2/inode.h
> index 0c22ddd..6e0633e 100644
> --- a/fs/ocfs2/inode.h
> +++ b/fs/ocfs2/inode.h
> @@ -43,9 +43,6 @@ struct ocfs2_inode_info
> /* protects extended attribute changes on this inode */
> struct rw_semaphore ip_xattr_sem;
>
> - /* Number of outstanding AIO's which are not page aligned */
> - struct mutex ip_unaligned_aio;
> -
> /* These fields are protected by ip_lock */
> spinlock_t ip_lock;
> u32 ip_open_count;
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index c70a80b..3fd171f 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -1723,7 +1723,6 @@ static void ocfs2_inode_init_once(void *data)
> INIT_LIST_HEAD(&oi->ip_io_markers);
> INIT_LIST_HEAD(&oi->ip_unwritten_list);
> oi->ip_dir_start_lookup = 0;
> - mutex_init(&oi->ip_unaligned_aio);
> init_rwsem(&oi->ip_alloc_sem);
> init_rwsem(&oi->ip_xattr_sem);
> mutex_init(&oi->ip_io_mutex);
>
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