linux-kernel - Re: [PATCH v2] ipc/sem: do not sleep with a spin lock held

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Date:   Mon, 3 Jan 2022 18:17:58 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Jiri Slaby <jirislaby@...nel.org>, cgel.zte@...il.com,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     stable@...r.kernel.org, arnd@...db.de, chi.minghao@....com.cn,
        dbueso@...e.de, linux-kernel@...r.kernel.org,
        rdunlap@...radead.org, shakeelb@...gle.com, unixbhaskar@...il.com,
        vvs@...tuozzo.com, zealci@....com.cn
Subject: Re: [PATCH v2] ipc/sem: do not sleep with a spin lock held

Hi Jiri,

On 1/3/22 10:27, Jiri Slaby wrote:
> On 23. 12. 21, 4:12, cgel.zte@...il.com wrote:
>> From: Minghao Chi <chi.minghao@....com.cn>
>>
>> We can't call kvfree() with a spin lock held, so defer it.
>
> Sorry, defer what?
>
First drop the spinlock, then call kvfree().


> There are attempts to fix kvfree instead, not sure which of these 
> approaches (fix kvfree or its callers) won in the end?
>
Exactly. We have three options - but noone volunteered yet to decide:

- change ipc/sem.c [minimal change]

- change kvfree() to use vfree_atomic() [would also fix other changes 
that did s/kfree/kvfree/]

- Modify the vma handling so that it becomes safe to call vfree() while 
holding a spinlock. [perfect approach, but I'm concerned about side effects]


--

     Manfred