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[124.209.188.1]) by smtp.gmail.com with ESMTPSA id b33-20020a630c21000000b004fbd91d9716sm9675797pgl.15.2023.04.19.01.23.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Apr 2023 01:23:16 -0700 (PDT) Date: Wed, 19 Apr 2023 17:23:11 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] printk: Enough to disable preemption in printk deferred context Message-ID: <20230419082311.GA1496740@google.com> References: <20230419074210.17646-1-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230419074210.17646-1-pmladek@suse.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A2F9A1C000B X-Rspam-User: X-Stat-Signature: xi1y45yhebyitrtch3ipi85ha9xsp36w X-HE-Tag: 1681892598-291899 X-HE-Meta: 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 zlEgcbaN kqqQlnVL3G7i/R9FwKY6/v9SC7kQDlIKQnIKO9uS2ymXkBKoyymGaQXaWRrCQ+Ehy+ofqG2DOUps3xi9QWVZrPBgXBHsubDSOEUEFzEb0Fl0LN6D3GxGUXcyNFh/cU8LFLrNgPQ2oVBc4gYCt01a9xHUGTdd+5+rMnGtyzX6qVfFdlUa+3AaX73XZB890xv7+vkJrplvBLiw7DBDtrbh+SC25z6lhpJDgvLmBTQKuk2WnPepVnDs8/Ibu2zk2GPqnh4+3qKL5PmUavF9B/IGoF6PoyOnnNa7WMy0nU0zflve5HsGPJSddWB3hFOVUHbq/QVo/TW8cLiS7lLYpgwp/H7N3bfLxIPOIbzAicKQTf188w/FHxmX7RvJPeb4qBhIw6zIZ+9FiFYseglA86A8og3n2BAGW+qO9R5lzfe3a3u/uHEz/uooIuZzP1BNppPDU75Cp 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 (23/04/19 09:42), 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. > > Fixes: 93d102f094be ("printk: remove safe buffers") > Signed-off-by: Petr Mladek Looks good to me Reviewed-by: Sergey Senozhatsky