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Mon, 11 May 2026 23:58:36 +0000 Message-ID: Date: Mon, 11 May 2026 16:58:34 -0700 User-Agent: Mozilla Thunderbird Subject: Re: unexpected auto-maintenance, was Re: git hogs the CPU, RAM and storage despite its config To: Jeff King CC: Taylor Blau , jean-christophe manciot , Patrick Steinhardt , , Derrick Stolee References: <20260508180341.GB737125@coredump.intra.peff.net> <20260509175249.GA2336928@coredump.intra.peff.net> <20260511200112.GA22912@coredump.intra.peff.net> <590781db-7c19-4aa8-8497-e16e5eb5eba1@intel.com> <20260511203502.GA25510@coredump.intra.peff.net> Content-Language: en-US From: Jacob Keller In-Reply-To: <20260511203502.GA25510@coredump.intra.peff.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0126.namprd04.prod.outlook.com (2603:10b6:303:84::11) To SN7PR11MB7592.namprd11.prod.outlook.com (2603:10b6:806:343::16) Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN7PR11MB7592:EE_|DS7PR11MB6150:EE_ X-MS-Office365-Filtering-Correlation-Id: e60438f6-dd4a-4358-5557-08deafb93741 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024|22082099003|18002099003|56012099003|11063799003; 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Though there is a bad sequence >>> where we delete somebody _else's_ lock, like: >>> >>> 1. Parent forks, but has not yet reassigned. >>> >>> 2. Child calls reassign to take ownership. Now both have >>> ownership. >>> >>> 3. Signal kills both parent and child, so they enter cleanup >>> code. >>> >>> 4. One of them (let's say the parent) deletes the lockfile. >>> >>> 5. Some other unrelated process (let's call it "git other") takes >>> the lock. >>> >>> 6. The child deletes the lockfile. >>> >>> And at that point "git other" thinks it holds the lock, but it >>> doesn't. It's quite an unlikely sequence in practice, though, I'd >>> think. >>> >>> - If neither claims ownership and a signal kills both, then nobody >>> cleans up the lock and it is left in place. This is annoying, but >>> also something that can happen occasionally anyway (kill -9, etc). >>> >>> I don't have an easy suggestion for making it more atomic, though. You >>> could choose one or the other direction using some synchronization >>> between the two (e.g., child reassigns only after parent signals over a >>> pipe that it has relinquished), but it's all kind of ugly. >>> >> Ya, that seems really ugly. My first thought was some way to disable >> signals temporarily, but I am guessing that either has no good way to do >> it or would introduce even more issues. Plus there is always kill -9... > > I guess the parent could relinquish control by reassigning to "0" before > even calling fork(), and then taking it back if fork() fails. And then > worst case is that nobody cleans up the lock (if the child is killed > before taking control), but that's the least-bad outcome from a > correctness perspective (though still annoying). > > -Peff This seems simpler than the suggestion of a pipe signal, and the worst result is only the version that is possible no matter what if there is a well timed kill -9.