linux-kernel - Re: [tip:locking/core] locking/rwsem: Enhance DEBUG_RWSEMS_WARN

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Date:   Fri, 19 Apr 2019 12:36:50 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     linux-kernel@...r.kernel.org, arnd@...db.de, longman@...hat.com,
        mingo@...nel.org, akpm@...ux-foundation.org, bp@...en8.de,
        a.p.zijlstra@...llo.nl, will.deacon@....com,
        tim.c.chen@...ux.intel.com, tglx@...utronix.de, hpa@...or.com,
        paulmck@...ux.vnet.ibm.com, dave@...olabs.net, dbueso@...e.de,
        torvalds@...ux-foundation.org, peterz@...radead.org
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON()
 macro

On Tue, Apr 16, 2019 at 03:04:41AM -0700, tip-bot for Waiman Long wrote:
> Commit-ID:  3b4ba6643d26a95e08067fca9a5da1828f9afabf
> Gitweb:     https://git.kernel.org/tip/3b4ba6643d26a95e08067fca9a5da1828f9afabf
> Author:     Waiman Long <longman@...hat.com>
> AuthorDate: Thu, 4 Apr 2019 13:43:15 -0400
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Wed, 10 Apr 2019 10:56:03 +0200
> 
> locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro
> 
> Currently, the DEBUG_RWSEMS_WARN_ON() macro just dumps a stack trace
> when the rwsem isn't in the right state. It does not show the actual
> states of the rwsem. This may not be that helpful in the debugging
> process.
> 
> Enhance the DEBUG_RWSEMS_WARN_ON() macro to also show the current
> content of the rwsem count and owner fields to give more information
> about what is wrong with the rwsem. The debug_locks_off() function is
> called as is done inside DEBUG_LOCKS_WARN_ON().
> 

This patch results in a large number of runtime warnings with several
architectures (at least arm, arm64, ppc, s390, sparc64, x86) if lock
debugging is enabled.

Example backtrace (ppc64):

DEBUG_RWSEMS_WARN_ON(sem->owner != current): count = 0x0, owner = 0x0, curr
0xc0000000012e0e00, list empty
WARNING: CPU: 0 PID: 0 at kernel/locking/rwsem.h:277 .up_write+0x138/0x150
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted
5.1.0-rc5-next-20190418-08527-g856544124538 #1
NIP:  c00000000015b7c8 LR: c00000000015b7c4 CTR: c0000000007b37a0
REGS: c00000000141f940 TRAP: 0700   Not tainted
(5.1.0-rc5-next-20190418-08527-g856544124538)
MSR:  8000000000029032 <SF,EE,ME,IR,DR,RI>  CR: 24000444  XER: 00000000
IRQMASK: 0 
GPR00: c00000000015b7c4 c00000000141fbd0 c00000000141ff00 000000000000006a 
GPR04: 0000000000000001 c000000000179fe8 0000000000000000 0000000000000001 
GPR08: c0000000012e0e00 0000000000000001 c00000000207ff00 0000000000000000 
GPR12: 0000000022000444 c000000002118000 000000003fde7ee0 0000000001fce4d8 
GPR16: 0000000001fce218 0000000001fce8f8 0000000002470000 0000000001fdcee8 
GPR20: 0000000000000000 fffffffffffffffd 0000000001fcea18 00000000ffffffff 
GPR24: 0000000001000000 c0000000014324bc c00000000104cf00 c00000000104c4f0 
GPR28: 0000000000000008 c000000000fd13d0 0000000000000000 c0000000012919b0 
NIP [c00000000015b7c8] .up_write+0x138/0x150
LR [c00000000015b7c4] .up_write+0x134/0x150
Call Trace:
[c00000000141fbd0] [c00000000015b7c4] .up_write+0x134/0x150 (unreliable)
[c00000000141fc60] [c000000000729808] .double_unlock_wsem+0x38/0x50
[c00000000141fce0] [c0000000007312f0] .dotest+0x88/0x7e8
[c00000000141fe20] [c00000000072f394] .locking_selftest+0x664/0x21e8
[c00000000141fed0] [c000000001102628] .start_kernel+0x4c4/0x640
[c00000000141ff90] [c00000000000aef0] start_here_common+0x1c/0x52c
Instruction dump:
7fe9fb78 e9490051 7fa95000 419e002c 3d02ffbd 39083bf8 3c82ffbd 3c62ffbd 
38843cc0 38633c50 4bf7bd81 60000000 <0fe00000> 4bffff64 3d02ffc2 39080e18 

Reverting the patch fixes the problem.

Bisect log (generated from ppc64 qemu run) attached.

Guenter

---
# bad: [856544124538f33105302451a9fbf0676598dddb] block: avoid scatterlist offsets > PAGE_SIZE
	Note: This was on top of next-20190418
# good: [dc4060a5dc2557e6b5aa813bf5b73677299d62d2] Linux 5.1-rc5
git bisect start 'HEAD' 'v5.1-rc5'
# good: [d49e1f8649c84f154e7df59300264f59b736f329] Merge remote-tracking branch 'crypto/master'
git bisect good d49e1f8649c84f154e7df59300264f59b736f329
# good: [06a21957e5c0aae87fb94b97ef965818bd7c9dac] Merge remote-tracking branch 'spi/for-next'
git bisect good 06a21957e5c0aae87fb94b97ef965818bd7c9dac
# bad: [c44f3caed068c67fe01056329e7e6cbf8f4920a8] Merge remote-tracking branch 'staging/staging-next'
git bisect bad c44f3caed068c67fe01056329e7e6cbf8f4920a8
# bad: [7b621018ce44727ffcc1f548187fead9e8fd6680] Merge remote-tracking branch 'usb-chipidea-next/ci-for-usb-next'
git bisect bad 7b621018ce44727ffcc1f548187fead9e8fd6680
# bad: [c8d9806ebb40150b6b4ee20f24ad0220fee7970a] Merge branch 'core/core'
git bisect bad c8d9806ebb40150b6b4ee20f24ad0220fee7970a
# good: [b9541e74fdc7673058c0db87dd9901aa10dda221] Merge branch 'perf/urgent'
git bisect good b9541e74fdc7673058c0db87dd9901aa10dda221
# bad: [408da98e8208df4664e775f393b1af9052ce61c6] Merge branch 'locking/core'
git bisect bad 408da98e8208df4664e775f393b1af9052ce61c6
# good: [cabf5ebbabcd4ad59b6eb216876c4c2e56fd3386] Merge tag 'perf-core-for-mingo-5.2-20190402' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core
git bisect good cabf5ebbabcd4ad59b6eb216876c4c2e56fd3386
# bad: [ad53fa10fa9e816067bbae7109845940f5e6df50] locking/qspinlock_stat: Introduce generic lockevent_*() counting APIs
git bisect bad ad53fa10fa9e816067bbae7109845940f5e6df50
# good: [f1887143f5984f23d2360f2efed6ef481bb41117] Documentation/atomic_t: Clarify signed vs unsigned
git bisect good f1887143f5984f23d2360f2efed6ef481bb41117
# good: [f7c2b7477bdc79a1e0cc3751a26c28031c1ab609] Merge branch 'lkmm-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/core
git bisect good f7c2b7477bdc79a1e0cc3751a26c28031c1ab609
# good: [12a30a7fc142a123c61da9623bd824d95d36c12e] locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h
git bisect good 12a30a7fc142a123c61da9623bd824d95d36c12e
# good: [a68e2c4c637918da47b3aa270051545cff7d8245] locking/rwsem: Add debug check for __down_read*()
git bisect good a68e2c4c637918da47b3aa270051545cff7d8245
# bad: [3b4ba6643d26a95e08067fca9a5da1828f9afabf] locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro
git bisect bad 3b4ba6643d26a95e08067fca9a5da1828f9afabf
# first bad commit: [3b4ba6643d26a95e08067fca9a5da1828f9afabf] locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro