From 5a85071c2cbcc7d8d8f764b33bf64c76e47d268d Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 21 Jun 2017 09:12:21 +1000 Subject: md: use a separate bio_set for synchronous IO. md devices allocate a bio_set and use it for two distinct purposes. mddev->bio_set is used to clone bios as part of sending upper level requests down to lower level devices, and it is also use for synchronous IO such as superblock and bitmap updates, and for correcting read errors. This multiple usage can lead to deadlocks. It is likely that cloned bios might be queued for write and to be waiting for a metadata update before the write can be permitted. If the cloning exhausted mddev->bio_set, the metadata update may not be able to proceed. This scenario has been seen during heavy testing, with lots of IO and lots of memory pressure. Address this by adding a new bio_set specifically for synchronous IO. All synchronous IO goes directly to the underlying device and is not queued at the md level, so request using entries from the new mddev->sync_set will complete in a timely fashion. Requests that use mddev->bio_set will sometimes need to wait for synchronous IO, but will no longer risk deadlocking that iO. Also: small simplification in mddev_put(): there is no need to wait until the spinlock is released before calling bioset_free(). Signed-off-by: NeilBrown Signed-off-by: Shaohua Li --- drivers/md/md.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'drivers/md/md.h') diff --git a/drivers/md/md.h b/drivers/md/md.h index 63d342d560b8..991f0fe2dcc6 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -444,6 +444,9 @@ struct mddev { struct attribute_group *to_remove; struct bio_set *bio_set; + struct bio_set *sync_set; /* for sync operations like + * metadata and bitmap writes + */ /* Generic flush handling. * The last to finish preflush schedules a worker to submit -- cgit v1.2.3