From: Matthew Wilcox <willy@infradead.org>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, elver@google.com, 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 19:49:00 -0800 [thread overview]
Message-ID: <20200211034900.GQ8731@bombadil.infradead.org> (raw)
In-Reply-To: <20200211030134.1847-1-cai@lca.pw>
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)
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 3:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 3:01 [PATCH v2] mm/filemap: fix a data race in filemap_fault() Qian Cai
2020-02-11 3:49 ` Matthew Wilcox [this message]
2020-02-11 3:55 ` Qian Cai
2020-02-11 13:24 ` Kirill A. Shutemov
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