On Sun, May 05, 2024 at 01:58:18AM +0000, Derrick Stolee via GitGitGadget wrote: > From: Derrick Stolee <stolee@xxxxxxxxx> > > During the latest v2.45.0 update, 'scalar reconfigure --all' started to > segfault on my machine. Breaking it down via the debugger, it was > faulting on a NULL reference to the_hash_algo, which is a macro pointing > to the_repository->hash_algo. > > This NULL reference appears to be due to the way the loop is abusing the > the_repository pointer, pointing it to a local repository struct after > discovering that the current directory is a valid Git repository. This > repo-swapping bit was in the original implementation from 4582676075 > (scalar: teach 'reconfigure' to optionally handle all registered > enlistments, 2021-12-03), but only recently started segfaulting while > trying to parse the HEAD reference. This also only happens on the > _second_ repository in the list, so does not reproduce if there is only > one registered repo. I think this explanation could use an update now that we have figured out the root cause likely being a detached HEAD, where `get_oid_hex()` will then access a NULL pointer. > My first inclination was to try to refactor cmd_reconfigure() to execute > 'git for-each-repo' instead of this loop. In addition to the difficulty > of executing 'scalar reconfigure' within 'git for-each-repo', it would > be difficult to perform the clean-up logic for non-existent repos if we > relied on that child process. > > Instead, I chose to move the temporary repo to be within the loop and > reinstate the_repository to its old value after we are done performing > logic on the current array item. > > Add tests to t9210-scalar.sh to test 'scalar reconfigure --all' with > multiple registered repos. There are two different ways that the old > use of the_repository could trigger bugs. These issues are being solved > independently to be more careful about the_repository being > uninitialized, but the change in this patch around the use of > the_repository is still a good safety precaution. > > Co-authored-by: Patrick Steinhardt <ps@xxxxxx> > Signed-off-by: Patrick Steinhardt <ps@xxxxxx> > Signed-off-by: Derrick Stolee <stolee@xxxxxxxxx> > --- > scalar: avoid segfault in reconfigure --all > > Update 'scalar reconfigure --all' to be more careful with the_repository > pointer, avoiding sudden halts in some scenarios. > > ------------------------------------------------------------------------ > > I noticed this while validating the v2.45.0 release (specifically the > microsoft/git fork, but this applies to the core project). > > Thanks, Patrick, for digging in and finding the critical reasons why > this issue can happen. I've included Patrick's test cases and given him > co-authorship. I forged his sign-off, so could you please ACK that > sign-off, Patrick? > > -Stolee Other than the above nit regarding the root cause analysis this patch looks good to me, and I'm fine with the forged SOB. Thanks! Patrick
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