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SubjectRe: KCSAN: data-race in __rcu_read_unlock / sync_rcu_exp_select_cpus
+RCU folks

On Mon, 4 Nov 2019 at 12:30, syzbot
<syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com> wrote:
>
> 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=1296ff50e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=99f4ddade3c22ab0cf23
> 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+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in __rcu_read_unlock / sync_rcu_exp_select_cpus
>
> read to 0xffffffff85a7d440 of 8 bytes by task 7624 on cpu 0:
> rcu_read_unlock_special kernel/rcu/tree_plugin.h:615 [inline]
> __rcu_read_unlock+0x381/0x3c0 kernel/rcu/tree_plugin.h:383
> rcu_read_unlock include/linux/rcupdate.h:652 [inline]
> filemap_map_pages+0x5b3/0x990 mm/filemap.c:2687
> do_fault_around mm/memory.c:3450 [inline]
> do_read_fault mm/memory.c:3484 [inline]
> do_fault mm/memory.c:3618 [inline]
> handle_pte_fault mm/memory.c:3849 [inline]
> __handle_mm_fault+0x2554/0x2cb0 mm/memory.c:3973
> handle_mm_fault+0x21b/0x530 mm/memory.c:4010
> do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
> __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
> do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
> page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202
>
> write to 0xffffffff85a7d440 of 8 bytes by task 7353 on cpu 1:
> sync_exp_reset_tree kernel/rcu/tree_exp.h:137 [inline]
> sync_rcu_exp_select_cpus+0xd5/0x590 kernel/rcu/tree_exp.h:427
> rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
> wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
> 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: 1 PID: 7353 Comm: kworker/1:0 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: rcu_gp wait_rcu_exp_gp
> ==================================================================
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 7353 Comm: kworker/1:0 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: rcu_gp wait_rcu_exp_gp
> 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_write8 kernel/kcsan/kcsan.c:36 [inline]
> __tsan_write8+0x32/0x40 kernel/kcsan/kcsan.c:36
> sync_exp_reset_tree kernel/rcu/tree_exp.h:137 [inline]
> sync_rcu_exp_select_cpus+0xd5/0x590 kernel/rcu/tree_exp.h:427
> rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
> wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
> 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
> Shutting down cpus with NMI
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
> This bug 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 bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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