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Mirsad Goran Todorovac fe48ba7dae workqueue: fix data race with the pwq->stats[] increment 
KCSAN has discovered a data race in kernel/workqueue.c:2598:

[ 1863.554079] ==================================================================
[ 1863.554118] BUG: KCSAN: data-race in process_one_work / process_one_work

[ 1863.554142] write to 0xffff963d99d79998 of 8 bytes by task 5394 on cpu 27:
[ 1863.554154] process_one_work (kernel/workqueue.c:2598)
[ 1863.554166] worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2752)
[ 1863.554177] kthread (kernel/kthread.c:389)
[ 1863.554186] ret_from_fork (arch/x86/kernel/process.c:145)
[ 1863.554197] ret_from_fork_asm (arch/x86/entry/entry_64.S:312)

[ 1863.554213] read to 0xffff963d99d79998 of 8 bytes by task 5450 on cpu 12:
[ 1863.554224] process_one_work (kernel/workqueue.c:2598)
[ 1863.554235] worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2752)
[ 1863.554247] kthread (kernel/kthread.c:389)
[ 1863.554255] ret_from_fork (arch/x86/kernel/process.c:145)
[ 1863.554266] ret_from_fork_asm (arch/x86/entry/entry_64.S:312)

[ 1863.554280] value changed: 0x0000000000001766 -> 0x000000000000176a

[ 1863.554295] Reported by Kernel Concurrency Sanitizer on:
[ 1863.554303] CPU: 12 PID: 5450 Comm: kworker/u64:1 Tainted: G             L     6.5.0-rc6+ #44
[ 1863.554314] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
[ 1863.554322] Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
[ 1863.554941] ==================================================================

    lockdep_invariant_state(true);
→   pwq->stats[PWQ_STAT_STARTED]++;
    trace_workqueue_execute_start(work);
    worker->current_func(work);

Moving pwq->stats[PWQ_STAT_STARTED]++; before the line

    raw_spin_unlock_irq(&pool->lock);

resolves the data race without performance penalty.

KCSAN detected at least one additional data race:

[  157.834751] ==================================================================
[  157.834770] BUG: KCSAN: data-race in process_one_work / process_one_work

[  157.834793] write to 0xffff9934453f77a0 of 8 bytes by task 468 on cpu 29:
[  157.834804] process_one_work (/home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2606)
[  157.834815] worker_thread (/home/marvin/linux/kernel/linux_torvalds/./include/linux/list.h:292 /home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2752)
[  157.834826] kthread (/home/marvin/linux/kernel/linux_torvalds/kernel/kthread.c:389)
[  157.834834] ret_from_fork (/home/marvin/linux/kernel/linux_torvalds/arch/x86/kernel/process.c:145)
[  157.834845] ret_from_fork_asm (/home/marvin/linux/kernel/linux_torvalds/arch/x86/entry/entry_64.S:312)

[  157.834859] read to 0xffff9934453f77a0 of 8 bytes by task 214 on cpu 7:
[  157.834868] process_one_work (/home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2606)
[  157.834879] worker_thread (/home/marvin/linux/kernel/linux_torvalds/./include/linux/list.h:292 /home/marvin/linux/kernel/linux_torvalds/kernel/workqueue.c:2752)
[  157.834890] kthread (/home/marvin/linux/kernel/linux_torvalds/kernel/kthread.c:389)
[  157.834897] ret_from_fork (/home/marvin/linux/kernel/linux_torvalds/arch/x86/kernel/process.c:145)
[  157.834907] ret_from_fork_asm (/home/marvin/linux/kernel/linux_torvalds/arch/x86/entry/entry_64.S:312)

[  157.834920] value changed: 0x000000000000052a -> 0x0000000000000532

[  157.834933] Reported by Kernel Concurrency Sanitizer on:
[  157.834941] CPU: 7 PID: 214 Comm: kworker/u64:2 Tainted: G             L     6.5.0-rc7-kcsan-00169-g81eaf55a60fc #4
[  157.834951] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
[  157.834958] Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
[  157.835567] ==================================================================

in code:

        trace_workqueue_execute_end(work, worker->current_func);
→       pwq->stats[PWQ_STAT_COMPLETED]++;
        lock_map_release(&lockdep_map);
        lock_map_release(&pwq->wq->lockdep_map);

which needs to be resolved separately.

Fixes: 725e8ec59c ("workqueue: Add pwq->stats[] and a monitoring script")
Cc: Tejun Heo <tj@kernel.org>
Suggested-by: Lai Jiangshan <jiangshanlai@gmail.com>
Link: https://lore.kernel.org/lkml/20230818194448.29672-1-mirsad.todorovac@alu.unizg.hr/
Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Signed-off-by: Tejun Heo <tj@kernel.org>
2023-08-29 09:52:16 -10:00
arch - Do FPU AP initialization on Xen PV too which got missed by the recent 2023-07-09 10:13:32 -07:00
block
certs
crypto
Documentation workqueue: Make default affinity_scope dynamically updatable 2023-08-07 15:57:25 -10:00
drivers
fs Minor cleanups for 6.5: 2023-07-09 09:50:42 -07:00
include workqueue: Make default affinity_scope dynamically updatable 2023-08-07 15:57:25 -10:00
init workqueue: Initialize unbound CPU pods later in the boot 2023-08-07 15:57:24 -10:00
io_uring
ipc
kernel workqueue: fix data race with the pwq->stats[] increment 2023-08-29 09:52:16 -10:00
lib workqueue: Fix cpu_intensive_thresh_us name in help text 2023-07-11 11:33:25 -10:00
LICENSES
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tools workqueue: Implement non-strict affinity scope for unbound workqueues 2023-08-07 15:57:25 -10:00
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.get_maintainer.ignore
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MAINTAINERS MAINTAINERS 2: Electric Boogaloo 2023-07-09 10:29:53 -07:00
Makefile Linux 6.5-rc1 2023-07-09 13:53:13 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.