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b=FKLRDDvRY/q1fMiGAUd4FZEFgUYN6iaYwCJHaXFT9xCLGODWkcM1MIiJICE7d99t5RVDqD fEQC9R987THCUyTUIbUvE6yFY5+lhorpFNW4Bru6n3smZfbXKplRoRP/PPIYFMVDZc127O SuM56Eq8P1SvQIg0XeqldtSGdmY7Gw0= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id BCF7B2C141; Wed, 19 Apr 2023 10:31:44 +0000 (UTC) Date: Wed, 19 Apr 2023 12:31:44 +0200 From: Petr Mladek To: Michal Hocko Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] printk: Enough to disable preemption in printk deferred context Message-ID: References: <20230419074210.17646-1-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: z3wdga1yacjshtmmim56tspk6bkybjn5 X-Rspamd-Queue-Id: BCB081C0012 X-HE-Tag: 1681900306-742250 X-HE-Meta: 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 GKxgfD1d zCGzYaWcH8hhGyRtg1RIKMfEHNDb92098v5KZB/7/lpN+O2XMmqMXyY4r0+nflmPLe22ZOYwm4wuHS4IoqLJo9mHqLWWd1CnPgnqiJNm53FrsHh53BkUZSHnD2SSIWFWsNveqWNHlhjNj4CHe5QAcUWwVLZCBRHEHuoqc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 2023-04-19 10:23:33, Michal Hocko wrote: > On Wed 19-04-23 09:42:10, Petr Mladek wrote: > > The comment above printk_deferred_enter()/exit() definition claims > > that it can be used only when interrupts are disabled. > > > > It was required by the original printk_safe_log_store() implementation. > > The code provided lockless synchronization between a single writer and > > a single reader. The interrupt and the normal context shared the same > > buffer. > > > > The commit 93d102f094be ("printk: remove safe buffers") removed > > these temporary buffers. Instead, the messages are stored directly into > > the new global lockless buffer which supports multiple parallel writers. > > > > As a result, it is safe to interrupt one writer now. The preemption still > > has to be disabled because the deferred context is CPU specific. > > Thanks for the clarification and explanation. > > > Fixes: 93d102f094be ("printk: remove safe buffers") > > Is this a fix though? I would expect some users to be changed from irq > to preempt to disabling to be considered a fix. Yeah, I am not sure about the Fixes tag either. I wanted to cross-link the two commits. But it is probably enough to mention it in the commit message. Best Regards, Petr