From: Michal Hocko <mhocko@kernel.org>
To: Vineet Gupta <vineet.gupta1@synopsys.com>
Cc: linux-snps-arc@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/2] ARC: show_regs: fix lockdep splat for good
Date: Thu, 20 Dec 2018 14:04:50 +0100 [thread overview]
Message-ID: <20181220130450.GB17350@dhcp22.suse.cz> (raw)
In-Reply-To: <1545159239-30628-3-git-send-email-vgupta@synopsys.com>
On Tue 18-12-18 10:53:59, Vineet Gupta wrote:
> signal handling core calls ARCH show_regs() with preemption disabled
> which causes __might_sleep functions such as mmput leading to lockdep
> splat. Workaround by re-enabling preemption temporarily.
>
> This may not be as bad as it sounds since the preemption disabling
> itself was introduced for a supressing smp_processor_id() warning in x86
> code by commit 3a9f84d354ce ("signals, debug: fix BUG: using
> smp_processor_id() in preemptible code in print_fatal_signal()")
The commit you are referring to here sounds dubious in itself. We do not
want to stick a preempt_disable just to silence a warning. show_regs is
called from preemptible context at several places (e.g. __warn). Maybe
this was not the case in 2009 when the change was introduced but this
seems like a relict from the past. So can we fix the actual problem
rather than build on top of it instead?
Or maybe I am just missing something here.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-12-20 13:04 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-18 18:53 [PATCH 0/2] ARC show_regs fixes Vineet Gupta
2018-12-18 18:53 ` [PATCH 1/2] ARC: show_regs: avoid page allocator Vineet Gupta
2018-12-19 17:04 ` Eugeniy Paltsev
2018-12-19 17:36 ` Vineet Gupta
2018-12-20 1:16 ` Vineet Gupta
2018-12-20 13:30 ` Tetsuo Handa
2018-12-20 18:36 ` Vineet Gupta
2018-12-20 18:43 ` Vineet Gupta
2018-12-19 20:46 ` William Kucharski
2018-12-19 21:36 ` Vineet Gupta
2018-12-20 12:57 ` Michal Hocko
2018-12-20 18:38 ` Vineet Gupta
2018-12-18 18:53 ` [PATCH 2/2] ARC: show_regs: fix lockdep splat for good Vineet Gupta
2018-12-20 13:04 ` Michal Hocko [this message]
2018-12-20 18:45 ` Vineet Gupta
2018-12-21 13:04 ` Michal Hocko
2018-12-21 13:27 ` Michal Hocko
2018-12-21 17:55 ` Vineet Gupta
2018-12-21 17:55 ` Vineet Gupta
2018-12-24 19:10 ` Michal Hocko
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