Commit a9501d74 authored by Song Liu's avatar Song Liu Committed by Shaohua Li
Browse files

md/r5cache: fix io_unit handling in r5l_log_endio() 



In r5l_log_endio(), once log->io_list_lock is released, the io unit
may be accessed (or even freed) by other threads. Current code
doesn't handle the io_unit properly, which leads to potential race
conditions.

This patch solves this race condition by:

1. Add a pending_stripe count flush_payload. Multiple flush_payloads
   are counted as only one pending_stripe. Flag has_flush_payload is
   added to show whether the io unit has flush_payload;
2. In r5l_log_endio(), check flags has_null_flush and
   has_flush_payload with log->io_list_lock held. After the lock
   is released, this IO unit is only accessed when we know the
   pending_stripe counter cannot be zeroed by other threads.

Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent b44886c5

drivers/md/raid5-cache.c

+31 −9
Original line number Diff line number Diff line
@@ -238,7 +238,8 @@ struct r5l_io_unit { 


	unsigned int has_flush:1;		/* include flush request */

	unsigned int has_fua:1;			/* include fua request */

	unsigned int has_null_flush:1; /* include empty flush request */

	unsigned int has_null_flush:1;		/* include null flush request */

	unsigned int has_flush_payload:1;	/* include flush payload  */

	/*

	 * io isn't sent yet, flush/fua request can only be submitted till it's

	 * the first IO in running_ios list
@@ -571,6 +572,8 @@ static void r5l_log_endio(struct bio *bio) 
	struct r5l_io_unit *io_deferred;

	struct r5l_log *log = io->log;

	unsigned long flags;

	bool has_null_flush;

	bool has_flush_payload;



	if (bio->bi_status)

		md_error(log->rdev->mddev, log->rdev);
@@ -580,6 +583,16 @@ static void r5l_log_endio(struct bio *bio) 


	spin_lock_irqsave(&log->io_list_lock, flags);

	__r5l_set_io_unit_state(io, IO_UNIT_IO_END);



	/*

	 * if the io doesn't not have null_flush or flush payload,

	 * it is not safe to access it after releasing io_list_lock.

	 * Therefore, it is necessary to check the condition with

	 * the lock held.

	 */

	has_null_flush = io->has_null_flush;

	has_flush_payload = io->has_flush_payload;



	if (log->need_cache_flush && !list_empty(&io->stripe_list))

		r5l_move_to_end_ios(log);

	else
@@ -600,18 +613,22 @@ static void r5l_log_endio(struct bio *bio) 
	if (log->need_cache_flush)

		md_wakeup_thread(log->rdev->mddev->thread);



	if (io->has_null_flush) {

	/* finish flush only io_unit and PAYLOAD_FLUSH only io_unit */

	if (has_null_flush) {

		struct bio *bi;



		WARN_ON(bio_list_empty(&io->flush_barriers));

		while ((bi = bio_list_pop(&io->flush_barriers)) != NULL) {

			bio_endio(bi);

			atomic_dec(&io->pending_stripe);

			if (atomic_dec_and_test(&io->pending_stripe)) {

				__r5l_stripe_write_finished(io);

				return;

			}

		}



	/* finish flush only io_unit and PAYLOAD_FLUSH only io_unit */

	if (atomic_read(&io->pending_stripe) == 0)

	}

	/* decrease pending_stripe for flush payload */

	if (has_flush_payload)

		if (atomic_dec_and_test(&io->pending_stripe))

			__r5l_stripe_write_finished(io);

}
@@ -881,6 +898,11 @@ static void r5l_append_flush_payload(struct r5l_log *log, sector_t sect) 
	payload->size = cpu_to_le32(sizeof(__le64));

	payload->flush_stripes[0] = cpu_to_le64(sect);

	io->meta_offset += meta_size;

	/* multiple flush payloads count as one pending_stripe */

	if (!io->has_flush_payload) {

		io->has_flush_payload = 1;

		atomic_inc(&io->pending_stripe);

	}

	mutex_unlock(&log->io_mutex);

}

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