[PATCH] direct-io: Fix sleep in atomic due to sync AIO

[PATCH] direct-io: Fix sleep in atomic due to sync AIO

[Jan Kara]

Commit e864f39569f4 "fs: add RWF_DSYNC aand RWF_SYNC" added additional
way for direct IO to become synchronous and thus trigger fsync from the
IO completion handler. Then commit 9830f4be159b "fs: Use RWF_* flags for
AIO operations" allowed these flags to be set for AIO as well. However
that commit forgot to update the condition checking whether the IO
completion handling should be defered to a workqueue and thus AIO DIO
with RWF_[D]SYNC set will call fsync() from IRQ context resulting in
sleep in atomic.

Fix the problem by checking directly iocb flags (the same way as it is
done in dio_complete()) instead of checking all conditions that could
lead to IO being synchronous.

CC: Christoph Hellwig <hch@lst.de>
CC: Goldwyn Rodrigues <rgoldwyn@suse.com>
CC: stable@vger.kernel.org
Reported-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 9830f4be159b29399d107bffb99e0132bc5aedd4
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/direct-io.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index a0ca9e48e993..1357ef563893 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1274,8 +1274,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	 */
 	if (dio->is_async && iov_iter_rw(iter) == WRITE) {
 		retval = 0;
-		if ((iocb->ki_filp->f_flags & O_DSYNC) ||
-		    IS_SYNC(iocb->ki_filp->f_mapping->host))
+		if (iocb->ki_flags & IOCB_DSYNC)
 			retval = dio_set_defer_completion(dio);
 		else if (!dio->inode->i_sb->s_dio_done_wq) {
 			/*
-- 
2.13.6

Re: [PATCH] direct-io: Fix sleep in atomic due to sync AIO

[Jens Axboe]

On Mon, Feb 26 2018, Jan Kara wrote:
> Commit e864f39569f4 "fs: add RWF_DSYNC aand RWF_SYNC" added additional
> way for direct IO to become synchronous and thus trigger fsync from the
> IO completion handler. Then commit 9830f4be159b "fs: Use RWF_* flags for
> AIO operations" allowed these flags to be set for AIO as well. However
> that commit forgot to update the condition checking whether the IO
> completion handling should be defered to a workqueue and thus AIO DIO
> with RWF_[D]SYNC set will call fsync() from IRQ context resulting in
> sleep in atomic.
> 
> Fix the problem by checking directly iocb flags (the same way as it is
> done in dio_complete()) instead of checking all conditions that could
> lead to IO being synchronous.

Thanks, applied.

-- 
Jens Axboe