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From: SeongJae Park <sjpark@amazon.com>
To: <gregkh@linuxfoundation.org>, <sashal@kernel.org>,
	<stable@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
	"Josef Bacik" <josef@toxicpanda.com>, Robert Stupp <snazy@gmx.de>,
	Minchan Kim <minchan@kernel.org>, Jan Kara <jack@suse.cz>
Subject: Re: [PATCH] mm: Don't bother dropping mmap_sem for zero size readahead
Date: Thu, 30 Jul 2020 13:34:35 +0200
Message-ID: <20200730113435.2280-1-sjpark@amazon.com> (raw)
In-Reply-To: <20200212101356.30759-1-jack@suse.cz>

Hello,


The commit fixed by this patch[1] was merged in v5.1 and this patch was merged
in the mainline in v5.7 (5c72feee3e45b40a3c96c7145ec422899d0e8964).  Thus, the
issue affects [v5.1, v5.6].  I was also able to reproduce the issue and confirm
the fix works on v5.4 based kernels.

However, I couldn't find this fix in neither latest stable/linux-5.4.y, nor
stable-queue/master.  Could you please put this patch in the queue?

[1] https://lore.kernel.org/linux-mm/20200212101356.30759-1-jack@suse.cz/


Thanks,
SeongJae Park

On Wed, 12 Feb 2020 11:13:56 +0100 Jan Kara <jack@suse.cz> wrote:

> When handling a page fault, we drop mmap_sem to start async readahead so
> that we don't block on IO submission with mmap_sem held.  However
> there's no point to drop mmap_sem in case readahead is disabled. Handle
> that case to avoid pointless dropping of mmap_sem and retrying the
> fault. This was actually reported to block mlockall(MCL_CURRENT)
> indefinitely.
> 
> Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations")
> Reported-by: Minchan Kim <minchan@kernel.org>
> Reported-by: Robert Stupp <snazy@gmx.de>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  mm/filemap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Andrew, could you please pick up this patch? Minchan also tripped over this
> bug...
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1146fcfa3215..3d39c437b07e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2458,7 +2458,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
>  	pgoff_t offset = vmf->pgoff;
>  
>  	/* If we don't want any read-ahead, don't bother */
> -	if (vmf->vma->vm_flags & VM_RAND_READ)
> +	if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
>  		return fpin;
>  	if (ra->mmap_miss > 0)
>  		ra->mmap_miss--;
> -- 
> 2.16.4


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 10:13 Jan Kara
2020-02-12 14:13 ` Josef Bacik
2020-02-12 16:16 ` Minchan Kim
2020-07-30 11:34 ` SeongJae Park [this message]
2020-08-01 10:39   ` Greg KH

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