Messages in this thread | | | Date | Wed, 22 Feb 2012 14:14:57 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take 2 |
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On 02/22/2012 10:19 AM, John Stultz wrote:
> On Wed, 2012-02-22 at 00:31 +0100, Rafael J. Wysocki wrote: >> Hi all, >> >> After the feedback so far I've decided to follow up with a refreshed patchset. >> The first two patches from the previous one went to linux-pm/linux-next >> and I included the recent evdev patch from Arve (with some modifications) >> to this patchset for completness. > > Hey Rafael, > Thanks again for posting this! I've started playing around with it in a > kvm environment, and got the following warning after echoing off > > autosleep: > ... > PM: resume of devices complete after 185.615 msecs > PM: Finishing wakeup. > Restarting tasks ... done. > PM: Syncing filesystems ... done. > PM: Preparing system for mem sleep > Freezing user space processes ... > Freezing of tasks failed after 20.01 seconds (1 tasks refusing to freeze, wq_busy=0): > bash D ffff880015714010
Ah.. I think I know what is the problem here..
The kernel was freezing userspace processes and meanwhile, you wrote "off" to autosleep. So, as a result, this userspace process (bash) just now entered kernel mode. Unfortunately, the autosleep_lock is held for too long, that is, something like:
acquire autosleep_lock modify autosleep_state <============== "A" pm_suspend or hibernate()
release autosleep_lock
At point marked "A", we should have released the autosleep lock and only then entered pm_suspend or hibernate(). Since the current code holds the lock and enters suspend/hibernate, the userspace process that wrote "off" to autosleep (or even userspace process that writes to /sys/power/state will end up waiting on autosleep_lock, thus failing the freezing operation.)
So the solution is to always release the autosleep lock before entering suspend/hibernation.
Regards, Srivatsa S. Bhat
> =============================== > [ INFO: suspicious RCU usage. ] > 3.3.0-rc3john+ #131 Not tainted > ------------------------------- > kernel/sched/core.c:4784 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 0 > 5 locks held by kworker/u:1/10: > #0: (autosleep){.+.+.+}, at: [<ffffffff81066db8>] process_one_work+0x2d8/0x8c0 > #1: (suspend_work){+.+.+.}, at: [<ffffffff81066db8>] process_one_work+0x2d8/0x8c0 > #2: (autosleep_lock){+.+.+.}, at: [<ffffffff810a2d3d>] try_to_suspend+0x2d/0xe0 > #3: (pm_mutex){+.+.+.}, at: [<ffffffff8109b9fc>] pm_suspend+0x8c/0x210 > #4: (tasklist_lock){.+.+..}, at: [<ffffffff8109b0f1>] try_to_freeze_tasks+0x2d1/0x400 > > stack backtrace: > Pid: 10, comm: kworker/u:1 Not tainted 3.3.0-rc3john+ #131 > Call Trace: > [<ffffffff81040d82>] ? vprintk+0x242/0x530 > [<ffffffff810b0fdb>] lockdep_rcu_suspicious+0xeb/0x100 > [<ffffffff81083371>] sched_show_task+0x121/0x180 > [<ffffffff8109b1e5>] try_to_freeze_tasks+0x3c5/0x400 > [<ffffffff810a2d10>] ? pm_autosleep_set_state+0x80/0x80 > [<ffffffff8109b2eb>] freeze_processes+0x3b/0xb0 > [<ffffffff8109baad>] pm_suspend+0x13d/0x210 > [<ffffffff810a2d5d>] try_to_suspend+0x4d/0xe0 > [<ffffffff81066f02>] process_one_work+0x422/0x8c0 > [<ffffffff81066db8>] ? process_one_work+0x2d8/0x8c0 > [<ffffffff810b063e>] ? put_lock_stats+0xe/0x40 > [<ffffffff81067a16>] worker_thread+0x476/0x550 > [<ffffffff810675a0>] ? rescuer_thread+0x200/0x200 > [<ffffffff810706fe>] kthread+0xae/0xc0 > [<ffffffff81af4cb4>] kernel_thread_helper+0x4/0x10 > [<ffffffff81af3078>] ? retint_restore_args+0x13/0x13 > [<ffffffff81070650>] ? __init_kthread_worker+0x70/0x70 > [<ffffffff81af4cb0>] ? gs_change+0x13/0x13 > 0 1981 1980 0x00020004 > ffff880015715d88 0000000000000046 ffff880015715c88 ffffffff8102c22b > ffff880015714010 ffff880015715fd8 ffff880015714010 ffff880015714000 > ffff880015715fd8 ffff880015714000 ffff880015c4e3c0 ffff88001342e540 > Call Trace: > [<ffffffff8102c22b>] ? kvm_clock_read+0x6b/0x90 > [<ffffffff810b1f2d>] ? mark_held_locks+0xad/0x150 > [<ffffffff81af10bf>] schedule+0x3f/0x60 > [<ffffffff81aef33b>] mutex_lock_nested+0x1cb/0x4c0 > [<ffffffff810a2cae>] ? pm_autosleep_set_state+0x1e/0x80 > [<ffffffff810a2cae>] ? pm_autosleep_set_state+0x1e/0x80 > [<ffffffff810a2cae>] pm_autosleep_set_state+0x1e/0x80 > [<ffffffff8109a74b>] autosleep_store+0x3b/0x80 > [<ffffffff813856e7>] kobj_attr_store+0x17/0x20 > [<ffffffff81200dcc>] sysfs_write_file+0xec/0x170 > [<ffffffff8118085f>] vfs_write+0x11f/0x1b0 > [<ffffffff811809f4>] sys_write+0x54/0xa0 > [<ffffffff81af4e66>] sysenter_dispatch+0x7/0x26 > [<ffffffff8139238e>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > Restarting tasks ... done. > > >
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