linux-toradex.git/block/blk-cgroup.c, branch v3.0.95

blk-cgroup: be able to remove the record of unplugged device

2011-10-03T18:40:42+00:00

commit d11bb4462c4cc6ddd45c6927c617ad79fa6fb8fc upstream.

The bug is we're not able to remove the device from blkio cgroup's
per-device control files if it gets unplugged.

To reproduce the bug:

  # mount -t cgroup -o blkio xxx /cgroup
  # cd /cgroup
  # echo "8:0 1000" > blkio.throttle.read_bps_device
  # unplug the device
  # cat blkio.throttle.read_bps_device
  8:0	1000
  # echo "8:0 0" > blkio.throttle.read_bps_device
  -bash: echo: write error: No such device

After patching, the device removal will succeed.

Thanks for the comments of Paul, Zefan, and Vivek.

Signed-off-by: Wanlong Gao 
Cc: Li Zefan 
Cc: Paul Menage 
Acked-by: Vivek Goyal 
Cc: Jens Axboe 
Signed-off-by: Andrew Morton 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman

cgroups: add per-thread subsystem callbacks

2011-05-27T00:12:34+00:00

Add cgroup subsystem callbacks for per-thread attachment in atomic contexts

Add can_attach_task(), pre_attach(), and attach_task() as new callbacks
for cgroups's subsystem interface.  Unlike can_attach and attach, these
are for per-thread operations, to be called potentially many times when
attaching an entire threadgroup.

Also, the old "bool threadgroup" interface is removed, as replaced by
this.  All subsystems are modified for the new interface - of note is
cpuset, which requires from/to nodemasks for attach to be globally scoped
(though per-cpuset would work too) to persist from its pre_attach to
attach_task and attach.

This is a pre-patch for cgroup-procs-writable.patch.

Signed-off-by: Ben Blum 
Cc: "Eric W. Biederman" 
Cc: Li Zefan 
Cc: Matt Helsley 
Reviewed-by: Paul Menage 
Cc: Oleg Nesterov 
Cc: David Rientjes 
Cc: Miao Xie 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

cfq-iosched: Make IO merge related stats per cpu

2011-05-23T08:02:19+00:00

Make BLKIO_STAT_MERGED per cpu hence gettring rid of need of taking
blkg->stats_lock.

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

blk-cgroup: Make cgroup stat reset path blkg->lock free for dispatch stats

2011-05-20T18:34:53+00:00

Now dispatch stats update is lock free. But reset of these stats still
takes blkg->stats_lock and is dependent on that. As stats are per cpu,
we should be able to just reset the stats on each cpu without any locks.
(Atleast for 64bit arch).

On 32bit arch there is a small race where 64bit updates are not atomic.
The result of this race can be that in the presence of other writers,
one might not get 0 value after reset of a stat and might see something
intermediate

One can write more complicated code to cover this race like sending IPI
to other cpus to reset stats and for offline cpus, reset these directly.

Right not I am not taking that path because reset_update is more of a
debug feature and it can happen only on 32bit arch and possibility of
it happening is small. Will fix it if it becomes a real problem. For
the time being going for code simplicity.

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

blk-cgroup: Make 64bit per cpu stats safe on 32bit arch

2011-05-20T18:34:53+00:00

Some of the stats are 64bit and updation will be non atomic on 32bit
architecture. Use sequence counters on 32bit arch to make reading
of stats safe.

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

blk-throttle: Make dispatch stats per cpu

2011-05-20T18:34:52+00:00

Currently we take blkg_stat lock for even updating the stats. So even if
a group has no throttling rules (common case for root group), we end
up taking blkg_lock, for updating the stats.

Make dispatch stats per cpu so that these can be updated without taking
blkg lock.

If cpu goes offline, these stats simply disappear. No protection has
been provided for that yet. Do we really need anything for that?

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

blk-cgroup: move some fields of unaccounted_time file under right config option

2011-05-20T18:34:52+00:00

cgroup unaccounted_time file is created only if CONFIG_DEBUG_BLK_CGROUP=y.
there are some fields which are out side this config option. Fix that.

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

blk-throttle: Use task_subsys_state() to determine a task's blkio_cgroup

2011-05-16T13:24:08+00:00

Currentlly we first map the task to cgroup and then cgroup to
blkio_cgroup. There is a more direct way to get to blkio_cgroup
from task using task_subsys_state(). Use that.

The real reason for the fix is that it also avoids a race in generic
cgroup code. During remount/umount rebind_subsystems() is called and
it can do following with and rcu protection.

cgrp->subsys[i] = NULL;

That means if somebody got hold of cgroup under rcu and then it tried
to do cgroup->subsys[] to get to blkio_cgroup, it would get NULL which
is wrong. I was running into this race condition with ltp running on a
upstream derived kernel and that lead to crash.

So ideally we should also fix cgroup generic code to wait for rcu
grace period before setting pointer to NULL. Li Zefan is not very keen
on introducing synchronize_wait() as he thinks it will slow
down moun/remount/umount operations.

So for the time being atleast fix the kernel crash by taking a more
direct route to blkio_cgroup.

One tester had reported a crash while running LTP on a derived kernel
and with this fix crash is no more seen while the test has been
running for over 6 days.

Signed-off-by: Vivek Goyal 
Reviewed-by: Li Zefan 
Signed-off-by: Jens Axboe

Fix common misspellings

2011-03-31T14:26:23+00:00

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi

blk-cgroup: Only give unaccounted_time under debug

2011-03-22T20:26:54+00:00

This change moves unaccounted_time to only be reported when
CONFIG_DEBUG_BLK_CGROUP is true.

Signed-off-by: Justin TerAvest 
Signed-off-by: Jens Axboe