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Date:   Mon, 04 Nov 2019 03:29:07 -0800
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Subject: KCSAN: data-race in process_srcu / synchronize_srcu
From:   syzbot <syzbot+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com>
To:     axboe@kernel.dk, elver@google.com, justin@coraid.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
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Hello,

syzbot found the following crash on:

HEAD commit:    05f22368 x86, kcsan: Enable KCSAN for x86
git tree:       https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=17ade7ef600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
dashboard link: https://syzkaller.appspot.com/bug?extid=08f3e9d26e5541e1ecf2
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in process_srcu / synchronize_srcu

write to 0xffffffff8604e8a0 of 8 bytes by task 17 on cpu 1:
  srcu_gp_end kernel/rcu/srcutree.c:533 [inline]
  srcu_advance_state kernel/rcu/srcutree.c:1146 [inline]
  process_srcu+0x207/0x780 kernel/rcu/srcutree.c:1237
  process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
  worker_thread+0xa0/0x800 kernel/workqueue.c:2415
  kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffffffff8604e8a0 of 8 bytes by task 12515 on cpu 0:
  srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
  synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
  fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
  process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
  worker_thread+0xa0/0x800 kernel/workqueue.c:2415
  kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events_unbound fsnotify_connector_destroy_workfn
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events_unbound fsnotify_connector_destroy_workfn
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0xf5/0x159 lib/dump_stack.c:113
  panic+0x210/0x640 kernel/panic.c:221
  kcsan_report.cold+0xc/0x10 kernel/kcsan/report.c:302
  __kcsan_setup_watchpoint+0x32e/0x4a0 kernel/kcsan/core.c:411
  __tsan_read8 kernel/kcsan/kcsan.c:36 [inline]
  __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:36
  srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
  synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
  fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
  process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
  worker_thread+0xa0/0x800 kernel/workqueue.c:2415
  kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


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