From: Qian Cai <cai@lca.pw>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Marco Elver <elver@google.com>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-kernel@vger.kernel.org,
"Kirill A . Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v2] mm/filemap: fix a data race in filemap_fault()
Date: Mon, 10 Feb 2020 22:55:45 -0500 [thread overview]
Message-ID: <2EFC8936-4569-418F-82EC-6F7868BEEAE2@lca.pw> (raw)
In-Reply-To: <20200211034900.GQ8731@bombadil.infradead.org>
> On Feb 10, 2020, at 10:49 PM, Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Feb 10, 2020 at 10:01:34PM -0500, Qian Cai wrote:
>> struct file_ra_state ra.mmap_miss could be accessed concurrently during
>> page faults as noticed by KCSAN,
>>
>> BUG: KCSAN: data-race in filemap_fault / filemap_map_pages
>>
>> write to 0xffff9b1700a2c1b4 of 4 bytes by task 3292 on cpu 30:
>> filemap_fault+0x920/0xfc0
>> do_sync_mmap_readahead at mm/filemap.c:2384
>> (inlined by) filemap_fault at mm/filemap.c:2486
>> __xfs_filemap_fault+0x112/0x3e0 [xfs]
>> xfs_filemap_fault+0x74/0x90 [xfs]
>> __do_fault+0x9e/0x220
>> do_fault+0x4a0/0x920
>> __handle_mm_fault+0xc69/0xd00
>> handle_mm_fault+0xfc/0x2f0
>> do_page_fault+0x263/0x6f9
>> page_fault+0x34/0x40
>>
>> read to 0xffff9b1700a2c1b4 of 4 bytes by task 3313 on cpu 32:
>> filemap_map_pages+0xc2e/0xd80
>> filemap_map_pages at mm/filemap.c:2625
>> do_fault+0x3da/0x920
>> __handle_mm_fault+0xc69/0xd00
>> handle_mm_fault+0xfc/0x2f0
>> do_page_fault+0x263/0x6f9
>> page_fault+0x34/0x40
>>
>> Reported by Kernel Concurrency Sanitizer on:
>> CPU: 32 PID: 3313 Comm: systemd-udevd Tainted: G W L 5.5.0-next-20200210+ #1
>> Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
>>
>> ra.mmap_miss is used to contribute the readahead decisions, a data race
>> could be undesirable. Both the read and write is only under
>> non-exclusive mmap_sem, two concurrent writers could even overflow the
>> counter. Fixing the underflow by writing to a local variable before
>> committing a final store to ra.mmap_miss given a small inaccuracy of the
>> counter should be acceptable.
>>
>> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name>
>> Signed-off-by: Qian Cai <cai@lca.pw>
>
> That's more than Suggested-by. The correct way to submit this patch is:
>
> From: Kirill A. Shutemov <kirill@shutemov.name>
> (at the top of the patch, so it gets credited to Kirill)
Sure, if Kirill is going to provide his Signed-off-by in the first place, I’ll be happy to
submit it on his behalf.
>
> then in this section:
>
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> Tested-by: Qian Cai <cai@lca.pw>
>
> And now you can add:
>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
next prev parent reply other threads:[~2020-02-11 3:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 3:01 Qian Cai
2020-02-11 3:49 ` Matthew Wilcox
2020-02-11 3:55 ` Qian Cai [this message]
2020-02-11 13:24 ` Kirill A. Shutemov
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