linux-kernel - Re: [PATCH v3] mm: fix unexpected changes to {failslab|fail_page

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Message-Id: <20221118134236.17a67804b3b6e6c157d8ea02@linux-foundation.org>
Date:   Fri, 18 Nov 2022 13:42:36 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     akinobu.mita@...il.com, dvyukov@...gle.com, jgg@...dia.com,
        willy@...radead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] mm: fix unexpected changes to
 {failslab|fail_page_alloc}.attr

On Fri, 18 Nov 2022 18:00:11 +0800 Qi Zheng <zhengqi.arch@...edance.com> wrote:

> When we specify __GFP_NOWARN, we only expect that no warnings
> will be issued for current caller. But in the __should_failslab()
> and __should_fail_alloc_page(), the local GFP flags alter the
> global {failslab|fail_page_alloc}.attr, which is persistent and
> shared by all tasks. This is not what we expected, let's fix it.
> 
> Cc: stable@...r.kernel.org
> Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Akinobu Mita <akinobu.mita@...il.com>
>
> ...
>
> -bool should_fail(struct fault_attr *attr, ssize_t size)
> +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags)
>  {
>  	bool stack_checked = false;
>  
> @@ -152,13 +149,20 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
>  		return false;
>  
>  fail:
> -	fail_dump(attr);
> +	if (!(flags & FAULT_NOWARN))
> +		fail_dump(attr);
>  
>  	if (atomic_read(&attr->times) != -1)
>  		atomic_dec_not_zero(&attr->times);
>  
>  	return true;
>  }
> +EXPORT_SYMBOL_GPL(should_fail_ex);

I don't see a need to export this?