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Wed, 7 Oct 2026 01:29:30 -0400 (EDT) Received: by mail (OpenSMTPD) with ESMTPSA id 7e408142 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 7 Oct 2026 05:29:29 +0000 (UTC) Date: Wed, 7 Oct 2026 07:29:26 +0200 From: Patrick Steinhardt To: Junio C Hamano Cc: git@vger.kernel.org, Guillaume Chauvel , Philippe Blain , "Mark C. Chu-Carroll" , Jeff King Subject: Re: [PATCH v2 2/2] packfile: fix corruption due to stale delta base cache entries Message-ID: References: <20261006-pks-packfile-stale-delta-base-cache-v2-0-69669a2fc6ce@pks.im> <20261006-pks-packfile-stale-delta-base-cache-v2-2-69669a2fc6ce@pks.im> Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Oct 06, 2026 at 12:57:41PM -0700, Junio C Hamano wrote: > Patrick Steinhardt writes: > > > Note that the added test reliably reproduces the above bug on my machine > > that uses NixOS at c59305bab206 (cosmic-applets: add missing runtime > > dependency (#566040), 2026-10-01) with glibc 2.44-25. But as we rely on > > specific allocation behaviour of glibc it is very likely that the test > > will not work on other platforms. > > In other words, the test will not detect the bug, when the fix is > reverted, unless the glibc allocator is used? It is specific to memory allocation patterns and thus to the platform, yes. But I just confirmed that the test also fails on for example Alpine Linux, so it even reproduces with musl libc. I haven't tested any other platforms though. > Adding an unreliable reproducer for a bug that is already fixed may be > of dubious value. However, even if the test is unreliable (since > other allocators might hide the bug when the fix is reverted), it may > be OK as long as it catches the bug on widely used configurations and > does not trigger false positives. Yeah, it at least catches the bug on some systems. And I think even if it eventually didn't anymore, it exercises a part of our system (doing submodule merges across many submodules) that wasn't previously exercised, I think. So it would still have some value there. > On the other hand, the earlier suggestion to write custom low-level > code to simulate a colliding allocation address somehow smells like a > maintenance burden to me. Agreed. It simply is too much boilerplate for too specific a failure, if you ask me. Patrick