On 05/11/2015 03:33 AM, Krzysztof Kozlowski wrote:
2015-03-12 18:11 GMT+09:00 Damian Eppel <d.eppel@xxxxxxxxxxx>:This is to fix an issue of sleeping in atomic context when processing hotplug notifications in Exynos MCT(Multi-Core Timer). The issue was reproducible on Exynos 3250 (Rinato board) and Exynos 5420 (Arndale Octa board). Whilst testing cpu hotplug events on kernel configured with DEBUG_PREEMPT and DEBUG_ATOMIC_SLEEP we get following BUG message, caused by calling request_irq() and free_irq() in the context of hotplug notification (which is in this case atomic context). root@target:~# echo 0 > /sys/devices/system/cpu/cpu1/online [ 25.157867] IRQ18 no longer affine to CPU1 ... [ 25.158445] CPU1: shutdown root@target:~# echo 1 > /sys/devices/system/cpu/cpu1/online [ 40.785859] CPU1: Software reset [ 40.786660] BUG: sleeping function called from invalid context at mm/slub.c:1241 [ 40.786668] in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/1 [ 40.786678] Preemption disabled at:[< (null)>] (null) [ 40.786681] [ 40.786692] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.19.0-rc4-00024-g7dca860 #36 [ 40.786698] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree) [ 40.786728] [<c0014a00>] (unwind_backtrace) from [<c0011980>] (show_stack+0x10/0x14) [ 40.786747] [<c0011980>] (show_stack) from [<c0449ba0>] (dump_stack+0x70/0xbc) [ 40.786767] [<c0449ba0>] (dump_stack) from [<c00c6124>] (kmem_cache_alloc+0xd8/0x170) [ 40.786785] [<c00c6124>] (kmem_cache_alloc) from [<c005d6f8>] (request_threaded_irq+0x64/0x128) [ 40.786804] [<c005d6f8>] (request_threaded_irq) from [<c0350b8c>] (exynos4_local_timer_setup+0xc0/0x13c) [ 40.786820] [<c0350b8c>] (exynos4_local_timer_setup) from [<c0350ca8>] (exynos4_mct_cpu_notify+0x30/0xa8) [ 40.786838] [<c0350ca8>] (exynos4_mct_cpu_notify) from [<c003b330>] (notifier_call_chain+0x44/0x84) [ 40.786857] [<c003b330>] (notifier_call_chain) from [<c0022fd4>] (__cpu_notify+0x28/0x44) [ 40.786873] [<c0022fd4>] (__cpu_notify) from [<c0013714>] (secondary_start_kernel+0xec/0x150) [ 40.786886] [<c0013714>] (secondary_start_kernel) from [<40008764>] (0x40008764) Solution: Clockevent irqs cannot be requested/freed every time cpu is hot-plugged/unplugged as CPU_STARTING/CPU_DYING notifications that signals hotplug or unplug events are sent with both preemption and local interrupts disabled. Since request_irq() may sleep it is moved to the initialization stage and performed for all possible cpus prior putting them online. Then, in the case of hotplug event the irq asociated with the given cpu will simply be enabled. Similarly on cpu unplug event the interrupt is not freed but just disabled. Note that after successful request_irq() call for a clockevent device associated to given cpu the requested irq is disabled (via disable_irq()). That is to make things symmetric as we expect hotplug event as a next thing (which will enable irq again). This should not pose any problems because at the time of requesting irq the clockevent device is not fully initialized yet, therefore should not produce interrupts at that point. For disabling an irq at cpu unplug notification disable_irq_nosync() is chosen which is a non-blocking function. This again shouldn't be a problem as prior sending CPU_DYING notification interrupts are migrated away from the cpu. Fixes: 7114cd749a12 ("clocksource: exynos_mct: use (request/free)_irq calls for local timer registration") Signed-off-by: Damian Eppel <d.eppel@xxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Reported-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> Tested-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> (Tested on Arndale Octa Board) Tested-by: Marcin Jabrzyk <m.jabrzyk@xxxxxxxxxxx> (Tested on Rinato B2 (Exynos 3250) board)Hi Daniel and Thomas, Do you have any comments on this patch? Could you pick it up?
Not yet. -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html