Messages in this thread | | | Date | Thu, 26 Aug 2010 16:51:55 +0100 (BST) | From | Mark Hills <> | Subject | cgroup: rmdir() does not complete |
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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.
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?
Or is it likely to be some other cause, and how best to find it?
Thanks
-- Mark
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