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Subjectmmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU
On Tue, Mar 09, 2010 at 07:16:03PM -0800, akpm@linux-foundation.org wrote:
> The mm-of-the-moment snapshot 2010-03-09-19-15 has been uploaded to
>
> http://userweb.kernel.org/~akpm/mmotm/
>
> and will soon be available at
>
> git://zen-kernel.org/kernel/mmotm.git
>
> It contains the following patches against 2.6.34-rc1:
>

With preempt and sleeping spinlock debugging on, I'm seeing a lot of warnings
about scheduling while atomic. Starts off with messages like

[ 0.572278] BUG: scheduling while atomic: swapper/1/0x00000002
[ 0.576004] 1 lock held by swapper/1:
[ 0.580002] #0: (rcu_read_lock){.+.+.+}, at: [<ffffffff811b6950>] kobject_uevent_env+0x363/0x4d0
[ 0.600001] Modules linked in:
[ 0.608003] Pid: 1, comm: swapper Not tainted 2.6.34-rc1-mm1-vanilla #1
[ 0.612001] Call Trace:
[ 0.616005] [<ffffffff810727fe>] ? __debug_show_held_locks+0x22/0x24
[ 0.620005] [<ffffffff810395ed>] __schedule_bug+0x77/0x7c
[ 0.624004] [<ffffffff812f4cc5>] schedule+0xcc/0x723
[ 0.628003] [<ffffffff812f55b6>] schedule_timeout+0x2d/0x28d
[ 0.632003] [<ffffffff8107315d>] ? mark_held_locks+0x4d/0x6b
[ 0.636004] [<ffffffff812f81e9>] ? _raw_spin_unlock_irq+0x30/0x5d
[ 0.640003] [<ffffffff810733de>] ? trace_hardirqs_on_caller+0x110/0x134
[ 0.644003] [<ffffffff812f4a0f>] wait_for_common+0xdc/0x152
[ 0.648003] [<ffffffff8103a43b>] ? default_wake_function+0x0/0x14
[ 0.652004] [<ffffffff812f4b28>] wait_for_completion+0x1d/0x1f
[ 0.656004] [<ffffffff8105cdf0>] call_usermodehelper_exec+0xad/0xfa
[ 0.660004] [<ffffffff81068429>] ? prepare_usermodehelper_creds+0x136/0x168
[ 0.664003] [<ffffffff811b6a37>] kobject_uevent_env+0x44a/0x4d0
[ 0.668003] [<ffffffff811b6950>] ? kobject_uevent_env+0x363/0x4d0
[ 0.672003] [<ffffffff811b6ac8>] kobject_uevent+0xb/0xd
[ 0.676002] [<ffffffff811b5e65>] kset_register+0x37/0x3f
[ 0.680004] [<ffffffff8123239a>] bus_register+0x11f/0x2b1
[ 0.684005] [<ffffffff8175973e>] platform_bus_init+0x2c/0x44
[ 0.688003] [<ffffffff817597b9>] driver_init+0x1d/0x29
[ 0.692004] [<ffffffff8172c69b>] kernel_init+0x12e/0x1e3
[ 0.696003] [<ffffffff81003be4>] kernel_thread_helper+0x4/0x10
[ 0.700004] [<ffffffff812f8794>] ? restore_args+0x0/0x30
[ 0.704003] [<ffffffff8172c56d>] ? kernel_init+0x0/0x1e3
[ 0.708002] [<ffffffff81003be0>] ? kernel_thread_helper+0x0/0x10

There are a lot of warnings along these lines during boot. This system did
boot *eventually* but it was in obvious trouble. The warnings appear to
be all around kobject_uevent_env acquiring the RCU lock and then going to
sleep. Most likely candidate problem patches in mmotm are

sysctl-fix-up-remaining-references-to-uevent_helper
sysctl-fix-up-remaining-references-to-uevent_helper-fix

But there are also a whole host of other sysctl-related changes around RCU in
there. The changelog implies that these patches are part of some long-lived
review process so I didn't delve too deeply. The people most likely to be
involved based on comments in the changelog are cc'd.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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