On Wed, Feb 25, 2026 at 01:56:02AM +0100, Alejandro Colomar wrote:
Steven wrote (Fri, 10 Jan 2025 08:03:31 -0500):
How can it lead to misjudgment? If you have two or more hashes matching, do
you really think they'll have the same subjects?
The possibility isn't zero. Statistically, it's quite low. However,
it's non-zero.
$ git log --format=tformat:'%s' | sort | uniq -c | sort | tail
248 Merge branch 'perf-urgent-for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
263 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
275 Merge branch 'x86-urgent-for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
293 Merge tag 'arm64-fixes' of
git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
314 Merge branch 'akpm' (patches from Andrew)
315 Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
318 Merge tag 'scsi-fixes' of
git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
324 Merge branch 'for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
369 Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
670 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
$ git log --format=tformat:'%s' | grep -v ^Merge | sort | uniq -c | sort | tail
grep: (standard input): binary file matches
22 drm/amd/display: Clean up some inconsistent indenting
25 Auto-update from upstream
26 [ARM] Update mach-types
26 pmdomain: Merge branch fixes into next
30 s390: update defconfigs
32 tools arch x86: Sync the msr-index.h copy with the kernel sources
38 [SPARC64]: Update defconfig.
52 mmc: Merge branch fixes into next
59 drm/i915: Convert wait_for(I915_READ(reg)) to intel_wait_for_register()
62 batman-adv: Start new development cycle
Subjects repeat every now and then, and the entropy in some subjects is
actually quite low.
If you include the commit date in a Fixes tag, then you preclude the
entire possibility of a commit reference clash, because you won't have
two patches committed in the same date with the same subject and same
hash (unless you *really* try)
The probability of a collision where two commits share both the same
abbreviated SHA1 and the same subject line is so astronomically low that it's
not a realistic concern.
For context, Linus himself pushed back on merely extending the 12-character
SHA1 abbreviation to 13. A change that wouldn't even break existing scripts.
Yet the proposal here is to introduce an entirely new date parameter that's
incompatible with the current format, all to address a scenario that is
unlikely in practice.
--
Thanks,
Sasha
