Messages in this thread | | | Date | Fri, 27 Aug 2010 09:56:39 +0900 | From | Daisuke Nishimura <> | Subject | Re: cgroup: rmdir() does not complete |
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Hi.
On Thu, 26 Aug 2010 16:51:55 +0100 (BST) Mark Hills <mark@pogo.org.uk> wrote:
> I am experiencing hung tasks when trying to rmdir() on a cgroup. One task > spins, others queue up behind it with the following: > > INFO: task soaked-cgroup:27257 blocked for more than 120 seconds. > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > soaked-cgrou D ffff8800058157c0 0 27257 29411 0x00000000 > ffff88004ffffdd8 0000000000000086 ffff88004ffffda8 ffff88004ffffeb8 > 0000000000000010 ffff880119813780 ffff88004ffffd48 ffff88004fffffd8 > ffff88004fffffd8 000000000000f9b0 00000000000157c0 ffff880137693268 > Call Trace: > [<ffffffff81115edb>] ? mntput_no_expire+0x24/0xe7 > [<ffffffff81427acd>] __mutex_lock_common+0x14d/0x1b4 > [<ffffffff81108a7c>] ? path_put+0x1d/0x22 > [<ffffffff81427b48>] __mutex_lock_slowpath+0x14/0x16 > [<ffffffff81427c4f>] mutex_lock+0x31/0x4b > [<ffffffff8110bdf8>] do_rmdir+0x74/0x102 > [<ffffffff8110bebd>] sys_rmdir+0x11/0x13 > [<ffffffff81009b02>] system_call_fastpath+0x16/0x1b > > Kernel is from Fedora, 2.6.33.6. In all cases the cgroup contains no > tasks. > > Commit ec64f5 ("fix frequent -EBUSY at rmdir") adds a busy wait loop to > the rmdir. It looks like what I am seeing here and indicates that some > cgroup subsystem is busy, indefinitely. > The commit had caused a bug about rmdir, but it was fixed by the commit 88703267. The fix was merged in 2.6.31, so it seems that you hit a new one...
> I have not worked out how to reproduce it quickly. My only way is to > complete a 'dd' command in the cgroup, but then the problem is so rare it > is slow progress. > > Documentation/cgroup.memory.txt describes how force_empty can be required > in some cases. Does this mean that with the patch above, these cases will > now spin on rmdir(), instead of returning -EBUSY? How can produce a > reliable test case requiring memory.force_empty to be used, to test this? > You don't need to touch "force_empty". rmdir() does what "force_empty" does.
> Or is it likely to be some other cause, and how best to find it? > What cgroup subsystem did you mount where the directory existed you tried to rmdir() first ? If you mounted several subsystems on the same hierarchy, can you mount them separately to narrow down the cause ?
Thanks, Daisuke Nishimura.
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