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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 24 Apr 2023 09:45:35 +0200
Message-ID: <CACT4Y+ZgJGNGEW==RPdUQRMHGP1GUT7f_Y6CKjvqjizX7Ty6YA@mail.gmail.com>
Subject: Re: [syzbot] [block?] KCSAN: data-race in __mod_timer / blk_add_timer (6)
To:     syzbot <syzbot+da80e6a47db00f8be22c@syzkaller.appspotmail.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
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On Mon, 24 Apr 2023 at 09:21, syzbot
<syzbot+da80e6a47db00f8be22c@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    148341f0a2f5 Merge tag 'vfs.misc.fixes.v6.3-rc6' of git://..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a5970dc80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=54d63ee086ae78d0
> dashboard link: https://syzkaller.appspot.com/bug?extid=da80e6a47db00f8be22c
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1c557f92a6e1/disk-148341f0.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f2c85210e1ce/vmlinux-148341f0.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b019d0447709/bzImage-148341f0.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+da80e6a47db00f8be22c@syzkaller.appspotmail.com

I did not fully grasp what happens here, but it looks fishy.
The comment on top of blk_add_timer() says "Notes: Each request has
its own timer". It looks like it's not true (?). A simple timer can't
ensure proper timeout for 2+ commands, right?


> ==================================================================
> BUG: KCSAN: data-race in __mod_timer / blk_add_timer
>
> write to 0xffff88810285dd20 of 8 bytes by task 26833 on cpu 0:
>  __mod_timer+0x625/0x890 kernel/time/timer.c:1121
>  mod_timer+0x1f/0x30 kernel/time/timer.c:1190
>  blk_add_timer+0x184/0x190 block/blk-timeout.c:164
>  blk_mq_start_request+0x100/0x2b0 block/blk-mq.c:1264
>  scsi_queue_rq+0x143b/0x1990 drivers/scsi/scsi_lib.c:1756
>  blk_mq_dispatch_rq_list+0x7b1/0x11f0 block/blk-mq.c:2059
>  __blk_mq_do_dispatch_sched block/blk-mq-sched.c:172 [inline]
>  blk_mq_do_dispatch_sched+0x4de/0x820 block/blk-mq-sched.c:186
>  __blk_mq_sched_dispatch_requests+0x1c1/0x260
>  blk_mq_sched_dispatch_requests+0x93/0x100 block/blk-mq-sched.c:338
>  __blk_mq_run_hw_queue+0x8e/0x110 block/blk-mq.c:2177
>  __blk_mq_delay_run_hw_queue+0xb3/0x3a0 block/blk-mq.c:2253
>  blk_mq_run_hw_queue+0x19f/0x330 block/blk-mq.c:2301
>  blk_mq_sched_insert_requests+0x1da/0x2c0 block/blk-mq-sched.c:492
>  blk_mq_dispatch_plug_list block/blk-mq.c:2748 [inline]
>  blk_mq_flush_plug_list+0x519/0x660 block/blk-mq.c:2790
>  __blk_flush_plug+0x223/0x280 block/blk-core.c:1153
>  blk_finish_plug+0x47/0x60 block/blk-core.c:1177
>  ext4_do_writepages+0x1c08/0x2140 fs/ext4/inode.c:2927
>  ext4_writepages+0x127/0x250 fs/ext4/inode.c:2964
>  do_writepages+0x1c5/0x340 mm/page-writeback.c:2551
>  filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:390
>  __filemap_fdatawrite_range mm/filemap.c:423 [inline]
>  file_write_and_wait_range+0xfa/0x190 mm/filemap.c:781
>  ext4_sync_file+0x10d/0x720 fs/ext4/fsync.c:151
>  vfs_fsync_range+0x10b/0x120 fs/sync.c:188
>  generic_write_sync include/linux/fs.h:2452 [inline]
>  ext4_buffered_write_iter+0x397/0x3e0 fs/ext4/file.c:296
>  ext4_file_write_iter+0xd7/0x10e0
>  do_iter_write+0x418/0x700 fs/read_write.c:861
>  vfs_iter_write+0x50/0x70 fs/read_write.c:902
>  iter_file_splice_write+0x456/0x7d0 fs/splice.c:778
>  do_splice_from fs/splice.c:856 [inline]
>  direct_splice_actor+0x84/0xa0 fs/splice.c:1022
>  splice_direct_to_actor+0x2ee/0x5f0 fs/splice.c:977
>  do_splice_direct+0x104/0x180 fs/splice.c:1065
>  do_sendfile+0x3b8/0x950 fs/read_write.c:1255
>  __do_sys_sendfile64 fs/read_write.c:1317 [inline]
>  __se_sys_sendfile64 fs/read_write.c:1309 [inline]
>  __x64_sys_sendfile64+0xbd/0x150 fs/read_write.c:1309
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff88810285dd20 of 8 bytes by task 2708 on cpu 1:
>  blk_add_timer+0x118/0x190
>  blk_mq_start_request+0x100/0x2b0 block/blk-mq.c:1264
>  scsi_queue_rq+0x143b/0x1990 drivers/scsi/scsi_lib.c:1756
>  blk_mq_dispatch_rq_list+0x7b1/0x11f0 block/blk-mq.c:2059
>  __blk_mq_do_dispatch_sched block/blk-mq-sched.c:172 [inline]
>  blk_mq_do_dispatch_sched+0x4de/0x820 block/blk-mq-sched.c:186
>  __blk_mq_sched_dispatch_requests+0x1c1/0x260
>  blk_mq_sched_dispatch_requests+0x93/0x100 block/blk-mq-sched.c:338
>  __blk_mq_run_hw_queue+0x8e/0x110 block/blk-mq.c:2177
>  __blk_mq_delay_run_hw_queue+0xb3/0x3a0 block/blk-mq.c:2253
>  blk_mq_run_hw_queue+0x19f/0x330 block/blk-mq.c:2301
>  blk_mq_sched_insert_requests+0x1da/0x2c0 block/blk-mq-sched.c:492
>  blk_mq_dispatch_plug_list block/blk-mq.c:2748 [inline]
>  blk_mq_flush_plug_list+0x519/0x660 block/blk-mq.c:2790
>  __blk_flush_plug+0x223/0x280 block/blk-core.c:1153
>  blk_finish_plug+0x47/0x60 block/blk-core.c:1177
>  jbd2_journal_commit_transaction+0x1c09/0x33f0 fs/jbd2/commit.c:797
>  kjournald2+0x242/0x420 fs/jbd2/journal.c:209
>  kthread+0x1ac/0x1e0 kernel/kthread.c:376
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
>
> value changed: 0x0000000100014674 -> 0x00000001000148f4
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 2708 Comm: jbd2/sda1-8 Not tainted 6.3.0-rc5-syzkaller-00005-g148341f0a2f5 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
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>
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