Messages in this thread Patch in this message | | | Subject | Re: [PATCH] ipc/sem: do not sleep with a spin lock held | From | Vasily Averin <> | Date | Wed, 22 Dec 2021 22:08:39 +0300 |
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On 22.12.2021 20:38, Vasily Averin wrote: > On 22.12.2021 20:06, Manfred Spraul wrote: >> Hi Vasily, >> >> On 12/22/21 16:50, Vasily Averin wrote: >>> On 22.12.2021 18:31, Vasily Averin wrote: >>>> On 22.12.2021 14:45, Manfred Spraul wrote: >>>>> Hi Minghao, >>>>> >>>>> On 12/22/21 09:10, cgel.zte@gmail.com wrote: >>>>>> From: Minghao Chi <chi.minghao@zte.com.cn> >>>>>> >>>>>> We can't call kvfree() with a spin lock held, so defer it. >>>> I'm sorry, but I do not understand why exactly we cannot use kvfree? >>>> Could you explain it in more details? >>> Got it, >>> there is cond_resched() called in __vfree() -> __vunmap() >>> >>> However I'm still not sure that in_interrupt() is used correctly here. >> >> I see three different topics: >> >> - is the current code violating the API? I think yes, thus there is a bug that needs to be fixed. > > I'm agree. Found issue is a bug and it should be fixed ASAP, > I'm sorry for a mistake in my patch. > >> - Where is __vunmap() sleeping? Would it be possible to make __vunmap() safe to be called when owning a spinlock? > > I think it is possible, and we should do it to prevent similar incidents in future. > vfree() should check preempt count to detect this situation (i.e. execution under taken spinlock) > generate WARN_ON and then call __vfree_deferred() to avoid sleep. > >> - should kvfree() use vfree() [i.e. unsafe when owning a spinlock] or vfree_atomic [i.e. a bit slower, but safe] > > I think it's better to change vfree.
I mean something like this:
--- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2674,7 +2674,7 @@ void vfree_atomic(const void *addr) static void __vfree(const void *addr) { - if (unlikely(in_interrupt())) + if (unlikely(in_atomic())) <<<< VvS: do not sleep in atomic ... __vfree_deferred(addr); else __vunmap(addr, 1); @@ -2703,7 +2703,7 @@ void vfree(const void *addr) kmemleak_free(addr); - might_sleep_if(!in_interrupt()); + might_sleep_if(in_task()); <<<<< VvS: ... but generate warning if vfree was called <<<<< in task context with taken spin_lock or spin_lock_bh if (!addr) return;
>> As we did quite many s/kfree/kvfree/ changes, perhaps just switching to vfree_atomic() is the best solution. >> >> @Andrew: What would you prefer? >> >> In addition, if we do not use vfree_atomic(): Then I would propose to copy the might_sleep_if() from vfree() into kvfree() > I think it does not help, as far as I understand we are in task context, just under taken spinlock. > > Thank you, > vasily Averin >
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