The following commit has been merged in the linux branch: commit f88fb981183e71daf40bbd84bc8251bbf7b59e19 Author: Kiyoshi Ueda k-ueda@ct.jp.nec.com Date: Fri Oct 16 23:18:15 2009 +0100
dm: dec_pending needs locking to save error value
Multiple instances of dec_pending() can run concurrently so a lock is needed when it saves the first error code.
I have never experienced actual problem without locking and just found this during code inspection while implementing the barrier support patch for request-based dm.
This patch adds the locking. I've done compile, boot and basic I/O testings.
Cc: stable@kernel.org Signed-off-by: Kiyoshi Ueda k-ueda@ct.jp.nec.com Signed-off-by: Jun'ichi Nomura j-nomura@ce.jp.nec.com Signed-off-by: Alasdair G Kergon agk@redhat.com
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index c5f9918..724efc6 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -47,6 +47,7 @@ struct dm_io { atomic_t io_count; struct bio *bio; unsigned long start_time; + spinlock_t endio_lock; };
/* @@ -578,8 +579,12 @@ static void dec_pending(struct dm_io *io, int error) struct mapped_device *md = io->md;
/* Push-back supersedes any I/O errors */ - if (error && !(io->error > 0 && __noflush_suspending(md))) - io->error = error; + if (unlikely(error)) { + spin_lock_irqsave(&io->endio_lock, flags); + if (!(io->error > 0 && __noflush_suspending(md))) + io->error = error; + spin_unlock_irqrestore(&io->endio_lock, flags); + }
if (atomic_dec_and_test(&io->io_count)) { if (io->error == DM_ENDIO_REQUEUE) { @@ -1226,6 +1231,7 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio) atomic_set(&ci.io->io_count, 1); ci.io->bio = bio; ci.io->md = md; + spin_lock_init(&ci.io->endio_lock); ci.sector = bio->bi_sector; ci.sector_count = bio_sectors(bio); if (unlikely(bio_empty_barrier(bio)))