From: Al Viro <viro@zeniv.linux.org.uk>
To: Qian Cai <cai@lca.pw>
Cc: hch@infradead.org, darrick.wong@oracle.com, elver@google.com,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs: fix a data race in i_size_write/i_size_read
Date: Wed, 19 Feb 2020 04:52:28 +0000 [thread overview]
Message-ID: <20200219045228.GO23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200219040426.1140-1-cai@lca.pw>
On Tue, Feb 18, 2020 at 11:04:26PM -0500, Qian Cai wrote:
> inode::i_size could be accessed concurently as noticed by KCSAN,
>
> BUG: KCSAN: data-race in iomap_do_writepage / iomap_write_end
>
> write to 0xffff8bf68fc0cac0 of 8 bytes by task 7484 on cpu 71:
> iomap_write_end+0xea/0x530
> i_size_write at include/linux/fs.h:888
> (inlined by) iomap_write_end at fs/iomap/buffered-io.c:782
> iomap_write_actor+0x132/0x200
> iomap_apply+0x245/0x8a5
> iomap_file_buffered_write+0xbd/0xf0
> xfs_file_buffered_aio_write+0x1c2/0x790 [xfs]
> xfs_file_write_iter+0x232/0x2d0 [xfs]
> new_sync_write+0x29c/0x3b0
> __vfs_write+0x92/0xa0
> vfs_write+0x103/0x260
> ksys_write+0x9d/0x130
> __x64_sys_write+0x4c/0x60
> do_syscall_64+0x91/0xb05
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> read to 0xffff8bf68fc0cac0 of 8 bytes by task 5901 on cpu 70:
> iomap_do_writepage+0xf4/0x450
> i_size_read at include/linux/fs.h:866
> (inlined by) iomap_do_writepage at fs/iomap/buffered-io.c:1558
> write_cache_pages+0x523/0xb20
> iomap_writepages+0x47/0x80
> xfs_vm_writepages+0xc7/0x100 [xfs]
> do_writepages+0x5e/0x130
> __writeback_single_inode+0xd5/0xb20
> writeback_sb_inodes+0x429/0x910
> __writeback_inodes_wb+0xc4/0x150
> wb_writeback+0x47b/0x830
> wb_workfn+0x688/0x930
> process_one_work+0x54f/0xb90
> worker_thread+0x80/0x5f0
> kthread+0x1cd/0x1f0
> ret_from_fork+0x27/0x50
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 70 PID: 5901 Comm: kworker/u257:2 Tainted: G L 5.6.0-rc2-next-20200218+ #2
> Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
> Workqueue: writeback wb_workfn (flush-254:0)
>
> The write is protected by exclusive inode::i_rwsem (in
> xfs_file_buffered_aio_write()) but the read is not. A shattered value
> could introduce a logic bug. Fixed it using a pair of WRITE/READ_ONCE().
If aligned 64bit stores on 64bit host (note the BITS_PER_LONG ifdefs) end up
being split, the kernel is FUBAR anyway. Details, please - how could that
end up happening?
next prev parent reply other threads:[~2020-02-19 4:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 4:04 [PATCH] fs: fix a data race in i_size_write/i_size_read Qian Cai
2020-02-19 4:52 ` Al Viro [this message]
2020-02-19 5:08 ` Qian Cai
2020-02-19 5:23 ` Al Viro
2020-02-19 9:21 ` Marco Elver
2020-02-19 12:18 ` David Sterba
2020-02-21 4:19 ` Qian Cai
2020-02-19 12:08 ` David Sterba
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