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Date: Sun, 6 Aug 2006 18:59:54 +0200 From: "Michal Piotrowski" <michal.k.k.piotrowski@...il.com> To: "Dave Jones" <davej@...hat.com>, "Linus Torvalds" <torvalds@...l.org>, "Michal Piotrowski" <michal.k.k.piotrowski@...il.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: 2.6.18-rc3-g3b445eea BUG: warning at /usr/src/linux-git/kernel/cpu.c:51/unlock_cpu_hotplug() Hi Dave, On 05/08/06, Dave Jones <davej@...hat.com> wrote: > On Fri, Aug 04, 2006 at 10:49:47PM -0400, Dave Jones wrote: > > This trace now makes a lot more sense to me. > > > CPU1 called lock_cpu_hotplug() for app cpuspeed. recursive_depth=0 > > [<c0104edc>] show_trace_log_lvl+0x58/0x152 > > [<c01054c2>] show_trace+0xd/0x10 > > [<c01055db>] dump_stack+0x19/0x1b > > [<c013e8c3>] lock_cpu_hotplug+0x39/0xbf > > [<c029fbae>] store_scaling_governor+0x142/0x1a3 > > [<c029f1a5>] store+0x37/0x48 > > [<c01a6561>] sysfs_write_file+0xab/0xd1 > > [<c016f99f>] vfs_write+0xab/0x157 > > [<c016ffe4>] sys_write+0x3b/0x60 > > [<c0103db9>] sysenter_past_esp+0x56/0x8d > > cpuspeed acquired cpu_bitmask_lock > > > > CPU1 called lock_cpu_hotplug() for app cpuspeed. recursive_depth=0 > > [<c0104edc>] show_trace_log_lvl+0x58/0x152 > > [<c01054c2>] show_trace+0xd/0x10 > > [<c01055db>] dump_stack+0x19/0x1b > > [<c013e8c3>] lock_cpu_hotplug+0x39/0xbf > > [<c0132f3c>] __create_workqueue+0x52/0x122 > > [<f901234b>] cpufreq_governor_dbs+0x9f/0x2c3 [cpufreq_ondemand] > > [<c029f7b6>] __cpufreq_governor+0x57/0xd8 > > [<c029f985>] __cpufreq_set_policy+0x14e/0x1bc > > [<c029fbc5>] store_scaling_governor+0x159/0x1a3 > > [<c029f1a5>] store+0x37/0x48 > > [<c01a6561>] sysfs_write_file+0xab/0xd1 > > [<c016f99f>] vfs_write+0xab/0x157 > > [<c016ffe4>] sys_write+0x3b/0x60 > > [<c0103db9>] sysenter_past_esp+0x56/0x8d > > Lukewarm IQ detected in hotplug locking > > BUG: warning at kernel/cpu.c:46/lock_cpu_hotplug() > > So when we write to sysfs to set the governor, we end up in store_scaling_governor() > which takes the hotplug lock, and then calls off into the governor to let it > do its thing. Part of ondemand's "thing" is to create a workqueue. > unfortunatly, __create_workqueue also takes the hotplug lock. > > Creating a variant of __create_workqueue that doesn't take the lock > seems really nasty. > > We could remove the locking from store_scaling_governor() and make the governors > themselves have to do the locking, but I'm not sure that's entirely safe. > > We could do something really disgusting like ... > > unlock_cpu_hotplug() > ... > create_workqueue() > ... > lock_cpu_hotplug() > > in ondemand, which opens up a tiny race window, but as ugly as it is, > looks to be the best solution of the bunch right now. > > Comments? > > The really sad part is this is completely unrelated to the original bug reported > in this thread, which shows just how widespread this braindamage is. > Michal's traces really don't really scream anything obvious to me. > (Though given it took me 4 hours to decode my own traces above, this is no > real sign of how big a problem this might be). > > Michal, could you apply this diff.. http://lkml.org/lkml/diff/2006/8/4/381/1 > (change the '120' to '60' first), and send me the debug spew that you get ? > You'll have to wait until a minute of uptime has passed. Oh, and edit > include/linux/jiffies.h to change INITIAL_JIFFIES to '0'. I hope that this one will help BUG: using smp_processor_id() in preemptible [00000001] code: cpuspeed/1433 caller is lock_cpu_hotplug+0x25/0xc5 [<fd95918f>] store_speed+0x36/0x9b [cpufreq_userspace] [<c029fa95>] store+0x37/0x48 [<c0104007>] show_trace_log_lvl+0x58/0x159 [<c0104765>] show_trace+0xd/0x10 [<c010482d>] dump_stack+0x19/0x1b [<c01fc842>] debug_smp_processor_id+0x96/0xac [<c01a8197>] sysfs_write_file+0xa6/0xcc [<c013e0db>] lock_cpu_hotplug+0x25/0xc5 [<fd95918f>] store_speed+0x36/0x9b [cpufreq_userspace] [<c029fa95>] store+0x37/0x48 [<c01a8197>] sysfs_write_file+0xa6/0xcc [<c0171577>] vfs_write+0xcd/0x179 [<c0171c20>] sys_write+0x3b/0x71 [<c010318d>] sysenter_past_esp+0x56/0x8d DWARF2 unwinder stuck at sysenter_past_esp+0x56/0x8d Leftover inexact backtrace: [<c0104765>] show_trace+0xd/0x10 [<c010482d>] dump_stack+0x19/0x1b [<c01fc842>] debug_smp_processor_id+0x96/0xac [<c013e0db>] lock_cpu_hotplug+0x25/0xc5 [<fd95918f>] store_speed+0x36/0x9b [cpufreq_userspace] [<c029fa95>] store+0x37/0x48 [<c01a8197>] [<c0171577>] vfs_write+0xcd/0x179 It's from 2.6.18-rc3-mm2. Config and dmesg log -> http://www.stardust.webpages.pl/files/mm/2.6.18-rc3-mm2/ > > Dave > > -- > http://www.codemonkey.org.uk > Regards, Michal -- Michal K. K. Piotrowski LTG - Linux Testers Group (http://www.stardust.webpages.pl/ltg/wiki/) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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