# git rev-parse -q --verify 55cb5f43689d7a9ea5bf35ef050f12334f197347^{commit}
55cb5f43689d7a9ea5bf35ef050f12334f197347
already have revision, skipping fetch
# git checkout -q -f -B kisskb 55cb5f43689d7a9ea5bf35ef050f12334f197347
# git clean -qxdf
# < git log -1
# commit 55cb5f43689d7a9ea5bf35ef050f12334f197347
# Merge: 9c749e61a110 b803d7c664d5
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Tue Dec 19 12:25:43 2023 -0800
# 
#     Merge tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
#     
#     Pull tracing fix from Steven Rostedt:
#      "While working on the ring buffer, I found one more bug with the
#       timestamp code, and the fix for this removed the need for the final
#       64-bit cmpxchg!
#     
#       The ring buffer events hold a "delta" from the previous event. If it
#       is determined that the delta can not be calculated, it falls back to
#       adding an absolute timestamp value. The way to know if the delta can
#       be used is via two stored timestamps in the per-cpu buffer meta data:
#     
#        before_stamp and write_stamp
#     
#       The before_stamp is written by every event before it tries to allocate
#       its space on the ring buffer. The write_stamp is written after it
#       allocates its space and knows that nothing came in after it read the
#       previous before_stamp and write_stamp and the two matched.
#     
#       A previous fix dd9394257078 ("ring-buffer: Do not try to put back
#       write_stamp") removed putting back the write_stamp to match the
#       before_stamp so that the next event could use the delta, but races
#       were found where the two would match, but not be for of the previous
#       event.
#     
#       It was determined to allow the event reservation to not have a valid
#       write_stamp when it is finished, and this fixed a lot of races.
#     
#       The last use of the 64-bit timestamp cmpxchg depended on the
#       write_stamp being valid after an interruption. But this is no longer
#       the case, as if an event is interrupted by a softirq that writes an
#       event, and that event gets interrupted by a hardirq or NMI and that
#       writes an event, then the softirq could finish its reservation without
#       a valid write_stamp.
#     
#       In the slow path of the event reservation, a delta can still be used
#       if the write_stamp is valid. Instead of using a cmpxchg against the
#       write stamp, the before_stamp needs to be read again to validate the
#       write_stamp. The cmpxchg is not needed.
#     
#       This updates the slowpath to validate the write_stamp by comparing it
#       to the before_stamp and removes all rb_time_cmpxchg() as there are no
#       more users of that function.
#     
#       The removal of the 32-bit updates of rb_time_t will be done in the
#       next merge window"
#     
#     * tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
#       ring-buffer: Fix slowpath of interrupted event
# < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-ld --version
# < git log --format=%s --max-count=1 55cb5f43689d7a9ea5bf35ef050f12334f197347
# make -s -j 40 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-  x86_64_defconfig
# < make -s -j 40 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-  help
# make -s -j 40 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-  olddefconfig
# make -s -j 40 ARCH=x86 O=/kisskb/build/linus_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-  
Completed OK
# rm -rf /kisskb/build/linus_x86_64_defconfig_x86_64-gcc8
# Build took: 0:01:29.667460