Re: [PATCH] ipc/sem: do not sleep with a spin lock held
From: Manfred Spraul
Date: Wed Dec 22 2021 - 12:06:50 EST
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@xxxxxxxxx wrote:
From: Minghao Chi <chi.minghao@xxxxxxxxxx>
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.
- Where is __vunmap() sleeping? Would it be possible to make __vunmap()
safe to be called when owning a spinlock?
- should kvfree() use vfree() [i.e. unsafe when owning a spinlock] or
vfree_atomic [i.e. a bit slower, but safe]
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()
--
Manfred