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b=pBGRzBhCwblY4cH5PfbPazP0AAH8fDx/EeOAVNkAAR9AfzJF0UKffpv6nfN8JLc0wKK8nq MdioBBmsdz4Tlk/WdgrZG6RgICd9lF91+9CXZtjciNUwCZ71K9WM2BWqZdu8KA6OKRjhxR HY18hGaovwsWjLT5L3MM5FgmY+idds0= 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 A179D2C141; Fri, 31 Mar 2023 08:05:51 +0000 (UTC) Date: Fri, 31 Mar 2023 10:05:48 +0200 From: Petr Mladek To: Sergey Senozhatsky Cc: Linus Torvalds , Peter Zijlstra , Luis Chamberlain , david@redhat.com, patches@lists.linux.dev, linux-modules@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, petr.pavlu@suse.com, prarit@redhat.com, gregkh@linuxfoundation.org, rafael@kernel.org, christophe.leroy@csgroup.eu, tglx@linutronix.de, song@kernel.org, rppt@kernel.org, willy@infradead.org, vbabka@suse.cz, mhocko@suse.com, dave.hansen@linux.intel.com Subject: Re: [PATCH 4/7] sempahore: add a helper for a concurrency limiter Message-ID: References: <20230329053149.3976378-1-mcgrof@kernel.org> <20230329053149.3976378-5-mcgrof@kernel.org> <20230329072112.GG4253@hirez.programming.kicks-ass.net> <20230329091935.GP4253@hirez.programming.kicks-ass.net> <20230330115626.GA124812@hirez.programming.kicks-ass.net> <20230331034209.GA12892@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230331034209.GA12892@google.com> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2ACB14001F X-Stat-Signature: skk11jq1pon9zzyzaush8iiqcy5j7qid X-HE-Tag: 1680249953-519780 X-HE-Meta: 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 v0+dX/Ep oEyfVfWFwjtFFJpA2WU77+m1jcg+lswcYBgGGxSlBEg4KdVRyBe51k/dSNed4E5P6gz/2QWxTryhQ4ivXTteawf/gYq6oVGySf7ga54XeD8lM5fSAQhhRhd4qnHUJSAUyTfiHLegiwjhdFWJlQzSw6qYpefM529xDqYJk 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 Fri 2023-03-31 12:42:09, Sergey Senozhatsky wrote: > On (23/03/30 09:23), Linus Torvalds wrote: > > Although we also do have some other issues - I think down_trylock() is > > ok in irq contexts, but mutex_trylock() is not. Maybe that's why > > printk uses semaphores? I forget. > > Yes, correct. IIRC we also cannot safely call mutex_unlock() from IRQ > context because it takes some internal mutex spin_lock in a non-IRQ-safe > manner. Semaphore is OK in this regard, both semaphore try_lock() and > unlock() can be called from IRQ. One more reason is that mutex must be released in the same context that took it. And printk() tries to pass console_sem() to another context. It was added by the commit dbdda842fe96 ("printk: Add console owner and waiter logic to load balance console writes"). It was relatively effective in reducing the risk of soft lockups. Best Regards, Petr