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From: Vladimir Sementsov-Ogievskiy To: qemu block Cc: qemu-devel , Max Reitz , Kevin Wolf , "Denis V. 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envelope-from=vsementsov@virtuozzo.com; helo=EUR02-HE1-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 23.02.2021 00:30, Vladimir Sementsov-Ogievskiy wrote: > Hi all! > > Thinking of how to prevent dereferencing to zero (and discard) of host cluster during flush of compressed cache (which I'm working on now), I have a question.. What prevents it for normal writes? > I have no idea about why didn't it fail for years.. May be, I'm missing something? I have idea of fixing: increase the refcount of host cluster before write to data_file (it's important to increase refacount in same s->lock critical section where we get host_offset) and dereference it after write.. It should help. Any thoughts? -- Best regards, Vladimir