KCSAN: data-race in blk_mq_get_request / blk_mq_get_request (3)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 245a4300 Merge branch 'rcu/kcsan' into tip/locking/kcsan
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=153f0269e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a4b9db179318d21f
dashboard link: https://syzkaller.appspot.com/bug?extid=65ef108ffd9024ade325
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [ax...@kernel.dk linux...@vger.kernel.org
linux-...@vger.kernel.org el...@google.com]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+65ef10...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blk_mq_get_request / blk_mq_get_request

write to 0xffff88812b30a548 of 8 bytes by task 21575 on cpu 0:
blk_mq_get_request+0x86d/0xac0 block/blk-mq.c:396
blk_mq_make_request+0x2d9/0xf60 block/blk-mq.c:1935
generic_make_request block/blk-core.c:1066 [inline]
generic_make_request+0x196/0x700 block/blk-core.c:1008
submit_bio+0x96/0x3c0 block/blk-core.c:1192
submit_bio_wait+0xb8/0x100 block/bio.c:975
blkdev_issue_flush+0x163/0x1c0 block/blk-flush.c:472
ext4_sync_file+0x6a8/0xaf0 fs/ext4/fsync.c:179
vfs_fsync_range+0x82/0x150 fs/sync.c:197
generic_write_sync include/linux/fs.h:2856 [inline]
ext4_buffered_write_iter+0x222/0x290 fs/ext4/file.c:259
ext4_file_write_iter+0xf4/0xd40 fs/ext4/file.c:547
call_write_iter include/linux/fs.h:1902 [inline]
do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
do_iter_write fs/read_write.c:970 [inline]
do_iter_write+0x13b/0x3c0 fs/read_write.c:951
vfs_iter_write+0x5c/0x80 fs/read_write.c:983
ovl_write_iter+0x366/0x550 fs/overlayfs/file.c:278
call_write_iter include/linux/fs.h:1902 [inline]
new_sync_write+0x388/0x4a0 fs/read_write.c:483
__vfs_write+0xb1/0xc0 fs/read_write.c:496
__kernel_write+0xb8/0x240 fs/read_write.c:515
write_pipe_buf+0xb6/0xf0 fs/splice.c:809
splice_from_pipe_feed fs/splice.c:512 [inline]
__splice_from_pipe+0x295/0x4a0 fs/splice.c:636
splice_from_pipe+0xbb/0x100 fs/splice.c:671
default_file_splice_write+0x45/0x90 fs/splice.c:821
do_splice_from fs/splice.c:863 [inline]
direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
do_splice_direct+0x161/0x1e0 fs/splice.c:1080
do_sendfile+0x384/0x7f0 fs/read_write.c:1464
__do_sys_sendfile64 fs/read_write.c:1519 [inline]
__se_sys_sendfile64 fs/read_write.c:1511 [inline]
__x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1511
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812b30a548 of 8 bytes by task 21569 on cpu 1:
blk_mq_get_request+0x85a/0xac0 block/blk-mq.c:396
blk_mq_make_request+0x2d9/0xf60 block/blk-mq.c:1935
generic_make_request block/blk-core.c:1066 [inline]
generic_make_request+0x196/0x700 block/blk-core.c:1008
submit_bio+0x96/0x3c0 block/blk-core.c:1192
submit_bio_wait+0xb8/0x100 block/bio.c:975
blkdev_issue_flush+0x163/0x1c0 block/blk-flush.c:472
ext4_sync_file+0x6a8/0xaf0 fs/ext4/fsync.c:179
vfs_fsync_range+0x82/0x150 fs/sync.c:197
generic_write_sync include/linux/fs.h:2856 [inline]
ext4_buffered_write_iter+0x222/0x290 fs/ext4/file.c:259
ext4_file_write_iter+0xf4/0xd40 fs/ext4/file.c:547
call_write_iter include/linux/fs.h:1902 [inline]
do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
do_iter_write fs/read_write.c:970 [inline]
do_iter_write+0x13b/0x3c0 fs/read_write.c:951
vfs_iter_write+0x5c/0x80 fs/read_write.c:983
ovl_write_iter+0x366/0x550 fs/overlayfs/file.c:278
call_write_iter include/linux/fs.h:1902 [inline]
new_sync_write+0x388/0x4a0 fs/read_write.c:483
__vfs_write+0xb1/0xc0 fs/read_write.c:496
__kernel_write+0xb8/0x240 fs/read_write.c:515
write_pipe_buf+0xb6/0xf0 fs/splice.c:809
splice_from_pipe_feed fs/splice.c:512 [inline]
__splice_from_pipe+0x295/0x4a0 fs/splice.c:636
splice_from_pipe+0xbb/0x100 fs/splice.c:671
default_file_splice_write+0x45/0x90 fs/splice.c:821
do_splice_from fs/splice.c:863 [inline]
direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
do_splice_direct+0x161/0x1e0 fs/splice.c:1080
do_sendfile+0x384/0x7f0 fs/read_write.c:1464
__do_sys_sendfile64 fs/read_write.c:1519 [inline]
__se_sys_sendfile64 fs/read_write.c:1511 [inline]
__x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1511
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21569 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.