linux-kernel - linux-next: tracebacks in workqueue.c/__flush

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Date:   Sat, 2 Feb 2019 14:20:23 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Tejun Heo <tj@...nel.org>
Subject: linux-next: tracebacks in workqueue.c/__flush_work()

Commit "workqueue: Try to catch flush_work() without INIT_WORK()" added
a warning if flush_work() is called without worker function.

This results in the following tracebacks, typically observed during
system shutdown.

------------[ cut here ]------------
WARNING: CPU: 0 PID: 101 at kernel/workqueue.c:3018 __flush_work+0x2a4/0x2e0
Modules linked in:
CPU: 0 PID: 101 Comm: umount Not tainted 5.0.0-rc4-next-20190201 #1
        fffffc0007dcbd18 0000000000000000 fffffc00003338a0 fffffc00003517d4
        fffffc00003517d4 fffffc0000e56c98 fffffc0000e56c98 fffffc0000ebc1d8
        fffffc0000ec0bd8 ffffffffa8024010 0000000000000bca 0000000000000000
        fffffc00003d3ea4 fffffc0000e56c98 fffffc0000e56c60 fffffc0000ebc1d8
        fffffc0000ec0bd8 0000000000000000 0000000000000001 0000000000000000
        fffffc000782d520 0000000000000000 fffffc000044ef50 fffffc0007c4b540
Trace:
[<fffffc00003338a0>] __warn+0x160/0x190
[<fffffc00003517d4>] __flush_work+0x2a4/0x2e0
[<fffffc00003517d4>] __flush_work+0x2a4/0x2e0
[<fffffc00003d3ea4>] lru_add_drain_all+0xe4/0x190
[<fffffc000044ef50>] shrink_dcache_sb+0x70/0xb0
[<fffffc0000478dc4>] invalidate_bh_lru+0x44/0x80
[<fffffc00003a94fc>] on_each_cpu_cond+0x5c/0x90
[<fffffc0000478d80>] invalidate_bh_lru+0x0/0x80
[<fffffc000047fe7c>] invalidate_bdev+0x3c/0x70
[<fffffc0000432ca8>] reconfigure_super+0x178/0x2c0
[<fffffc000045ee64>] ksys_umount+0x664/0x680
[<fffffc000045ee9c>] sys_umount+0x1c/0x30
[<fffffc00003115d4>] entSys+0xa4/0xc0
[<fffffc00003115d4>] entSys+0xa4/0xc0

---[ end trace 613cea34708701f1 ]---

The problem is seen with several (but not all) architectures. Affected
architectures/platforms are:
	alpha
	arm:versatilepb
	m68k
	mips, mips64 (boot from IDE drive or MMC, SMP disabled)
	parisc (nosmp builds)
	sparc, sparc64 (nosmp builds)

There may be others; several of my tests fail with build failures.

If/when it is seen, the problem is persistent.

Common denominator seems to be that SMP is disabled. It does appear that
for_each_cpu() ignores the mask for nosmp builds, but I don't really
understand why.

Guenter