Messages in this thread |  | | Subject | Re: [PATCH 1/5] perf/arm-cci: Fix CPU hotplug race avoidance | From | Suzuki K Poulose <> | Date | Tue, 5 Feb 2019 11:19:55 +0000 |
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Robin,
On 04/02/2019 17:09, Robin Murphy wrote: > The arm-cci probe logic faces a cyclic dependency wherein it has to pick > a valid CPU to associate with before registering the PMU device, has to > have the PMU state initialised before handling hotplug events in case it > must be migrated, but has to have the hotplug notifier registered before > the chosen CPU may go offline lest things get out of sync. The present > code has tried to solve the races by using get_cpu() to pick the current > CPU and prevent it from disappearing while the other two registrations > are performed, but that results in taking mutexes with preemption > disabled, which makes certain configurations very unhappy: > > [ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004 > [ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0 > [ 1.983342] Preemption disabled at: > [ 1.983353] [<ffffff80089801f4>] cci_pmu_probe+0x1dc/0x488 > [ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1 > [ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT) > [ 1.983364] Call trace: > [ 1.983369] dump_backtrace+0x0/0x158 > [ 1.983372] show_stack+0x24/0x30 > [ 1.983378] dump_stack+0x80/0xa4 > [ 1.983383] ___might_sleep+0x138/0x160 > [ 1.983386] __might_sleep+0x58/0x90 > [ 1.983391] __rt_mutex_lock_state+0x30/0xc0 > [ 1.983395] _mutex_lock+0x24/0x30 > [ 1.983400] perf_pmu_register+0x2c/0x388 > [ 1.983404] cci_pmu_probe+0x2bc/0x488 > [ 1.983409] platform_drv_probe+0x58/0xa8 > > However, we don't actually mind being preempted or migrated at this > point; all that really matters is that whichever CPU we pick does not > get offlined before we're done. Thus, do the robust thing and instead > take the lock to inhibit CPU hotplug for the duration. This also > revealed an additional race in assigning the global pointer too late > relative to the hotplug notifier, so that gets fixed in the process. > > Reported-by: "Li, Meng" <Meng.Li@windriver.com> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Thanks for fixing the issues.
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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