[Nbd] [PATCH 0/6] block: reread partitions changes and fix for loop

[Ming Lei <ming.lei@...1301...>]

Recently there are several reports about loop partition scanning
failure[1][2].

For loop, the root cause is one ABBA and one AA lock dependency
issue, and the two are fixed by patch 2 and patch 3 each.

Another reason is from the trylock in blkdev_reread_part(), which
may cause partition scanning failure too sometimes when another task
is holding the bd_mutex. In the discussion[1], both Tejun and Christoph
suggests to replace the trylock with mutex_lock in blkdev_reread_part(),
also Christoph suggests to export blkdev_reread_part.

Following the discussion, this patchset exports blkdev_reread_part(), and
introduces blkdev_reread_part_nolock() for fixing loop's AA lock issue.
Then ioctl_by_bdev(BLKRRPART) in loop, nbd and dasd is replaced with
blkdev_reread_part(). In the last patch, trylock in __blkdev_reread_part()
is replaced with mutex_lock, and some analysis is provided about the conversion.


[1], https://lkml.org/lkml/2015/1/26/137
[2], https://lkml.org/lkml/2015/3/31/888

Thanks,
Ming Lei