[PATCH v3 0/7] block: reread partitions changes and fix for loop

[Ming Lei]

Hi Guys,

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() 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.

V3:
	- fix lock unbalance in loop (2/7)
	- add reviewed-by from Christoph
	- run xfstest over loop and it passed
	- enable lockdep for verifying lock changes, and no warning
	with some common tests over loop block 

V2:
	- only print debug message in case of error (7/7)
	- add tested-by, acked-by

V1:
	- introduce __blkdev_reread_part(), and use lockdep_assert_held()(1/7)
	- replace lo_open_mutex with atomic reference count, plus freezing queue(2/7)
	- add comment about detecting release path(3/7)
	- remove dead code in dasd(7/7)

 block/ioctl.c                   | 37 ++++++++++++++++++++++++++++++++-----
 drivers/block/loop.c            | 51 ++++++++++++++++++++++++++++++++++++++-------------
 drivers/block/loop.h            |  2 +-
 drivers/block/nbd.c             |  2 +-
 drivers/s390/block/dasd_genhd.c | 19 +++++--------------
 include/linux/fs.h              |  3 +++
 6 files changed, 80 insertions(+), 34 deletions(-)


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

Thanks,
Ming Lei


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