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  • Bryan O'Donoghue Bryan O'Donoghue bryan.odonoghue
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  1. Mar 30, 2021
  3. Jan 17, 2021
  5. Nov 12, 2020
  7. Oct 05, 2020
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  21. Jul 18, 2020
    • Boris Burkov's avatar
      blk-cgroup: show global disk stats in root cgroup io.stat · ef45fe47
      Boris Burkov authored 
      
In order to improve consistency and usability in cgroup stat accounting,
we would like to support the root cgroup's io.stat.

Since the root cgroup has processes doing io even if the system has no
explicitly created cgroups, we need to be careful to avoid overhead in
that case.  For that reason, the rstat algorithms don't handle the root
cgroup, so just turning the file on wouldn't give correct statistics.

To get around this, we simulate flushing the iostat struct by filling it
out directly from global disk stats. The result is a root cgroup io.stat
file consistent with both /proc/diskstats and io.stat.

Note that in order to collect the disk stats, we needed to iterate over
devices. To facilitate that, we had to change the linkage of a disk_type
to external so that it can be used from blk-cgroup.c to iterate over
disks.

Suggested-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarBoris Burkov <boris@bur.io>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      ef45fe47
  23. Jul 08, 2020
  25. Jun 24, 2020
    • Luis Chamberlain's avatar
      block: revert back to synchronous request_queue removal · e8c7d14a
      Luis Chamberlain authored 
      
Commit dc9edc44 ("block: Fix a blk_exit_rl() regression") merged on
v4.12 moved the work behind blk_release_queue() into a workqueue after a
splat floated around which indicated some work on blk_release_queue()
could sleep in blk_exit_rl(). This splat would be possible when a driver
called blk_put_queue() or blk_cleanup_queue() (which calls blk_put_queue()
as its final call) from an atomic context.

blk_put_queue() decrements the refcount for the request_queue kobject, and
upon reaching 0 blk_release_queue() is called. Although blk_exit_rl() is
now removed through commit db6d9952 ("block: remove request_list code")
on v5.0, we reserve the right to be able to sleep within
blk_release_queue() context.

The last reference for the request_queue must not be called from atomic
context. *When* the last reference to the request_queue reaches 0 varies,
and so let's take the opportunity to document when that is expected to
happen and also document the context of the related calls as best as
possible so we can avoid future issues, and with the hopes that the
synchronous request_queue removal sticks.

We revert back to synchronous request_queue removal because asynchronous
removal creates a regression with expected userspace interaction with
several drivers. An example is when removing the loopback driver, one
uses ioctls from userspace to do so, but upon return and if successful,
one expects the device to be removed. Likewise if one races to add another
device the new one may not be added as it is still being removed. This was
expected behavior before and it now fails as the device is still present
and busy still. Moving to asynchronous request_queue removal could have
broken many scripts which relied on the removal to have been completed if
there was no error. Document this expectation as well so that this
doesn't regress userspace again.

Using asynchronous request_queue removal however has helped us find
other bugs. In the future we can test what could break with this
arrangement by enabling CONFIG_DEBUG_KOBJECT_RELEASE.

While at it, update the docs with the context expectations for the
request_queue / gendisk refcount decrement, and make these
expectations explicit by using might_sleep().

Fixes: dc9edc44 ("block: Fix a blk_exit_rl() regression")
Suggested-by: default avatarNicolai Stange <nstange@suse.de>
Signed-off-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: yu kuai <yukuai3@huawei.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      e8c7d14a
    • Luis Chamberlain's avatar
      block: clarify context for refcount increment helpers · 763b5892
      Luis Chamberlain authored 
      
Let us clarify the context under which the helpers to increment the
refcount for the gendisk and request_queue can be called under. We
make this explicit on the places where we may sleep with might_sleep().

We don't address the decrement context yet, as that needs some extra
work and fixes, but will be addressed in the next patch.

Signed-off-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      763b5892
    • Luis Chamberlain's avatar
      block: add docs for gendisk / request_queue refcount helpers · b5bd357c
      Luis Chamberlain authored 
      
This adds documentation for the gendisk / request_queue refcount
helpers.

Signed-off-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      b5bd357c
  27. May 27, 2020
  29. May 19, 2020
  31. May 13, 2020
  33. May 09, 2020
  35. Apr 20, 2020
  37. Mar 27, 2020
  39. Mar 25, 2020
  41. Mar 24, 2020