Buildresult: linus/or1ksim_defconfig/or32-gcc9 built on Oct 4, 11:01

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Status:	OK
Date/Time:	Oct 4, 11:01
Duration:	0:00:21.673563
Builder:	ka4
Revision:	sched: psi: fix bogus pressure spikes from aggregation race (`3840cbe24cf060ea05a585ca497814609f5d47d1)`
Target:	linus/or1ksim_defconfig/or32-gcc9
Branch:	linus
Compiler:	or32-gcc9 (or1k-linux-gcc (GCC) 9.4.0 / GNU ld (GNU Binutils) 2.36.1)
Config:	or1ksim_defconfig (download)
Log:	Download original No warnings found in log. Full Log # git rev-parse -q --verify 3840cbe24cf060ea05a585ca497814609f5d47d1^{commit} 3840cbe24cf060ea05a585ca497814609f5d47d1 already have revision, skipping fetch # git checkout -q -f -B kisskb 3840cbe24cf060ea05a585ca497814609f5d47d1 # git clean -qxdf # < git log -1 # commit 3840cbe24cf060ea05a585ca497814609f5d47d1 # Author: Johannes Weiner <hannes@cmpxchg.org> # Date: Thu Oct 3 07:29:05 2024 -0400 # # sched: psi: fix bogus pressure spikes from aggregation race # # Brandon reports sporadic, non-sensical spikes in cumulative pressure # time (total=) when reading cpu.pressure at a high rate. This is due to # a race condition between reader aggregation and tasks changing states. # # While it affects all states and all resources captured by PSI, in # practice it most likely triggers with CPU pressure, since scheduling # events are so frequent compared to other resource events. # # The race context is the live snooping of ongoing stalls during a # pressure read. The read aggregates per-cpu records for stalls that # have concluded, but will also incorporate ad-hoc the duration of any # active state that hasn't been recorded yet. This is important to get # timely measurements of ongoing stalls. Those ad-hoc samples are # calculated on-the-fly up to the current time on that CPU; since the # stall hasn't concluded, it's expected that this is the minimum amount # of stall time that will enter the per-cpu records once it does. # # The problem is that the path that concludes the state uses a CPU clock # read that is not synchronized against aggregators; the clock is read # outside of the seqlock protection. This allows aggregators to race and # snoop a stall with a longer duration than will actually be recorded. # # With the recorded stall time being less than the last snapshot # remembered by the aggregator, a subsequent sample will underflow and # observe a bogus delta value, resulting in an erratic jump in pressure. # # Fix this by moving the clock read of the state change into the seqlock # protection. This ensures no aggregation can snoop live stalls past the # time that's recorded when the state concludes. # # Reported-by: Brandon Duffany <brandon@buildbuddy.io> # Link: https://bugzilla.kernel.org/show_bug.cgi?id=219194 # Link: https://lore.kernel.org/lkml/20240827121851.GB438928@cmpxchg.org/ # Fixes: df77430639c9 ("psi: Reduce calls to sched_clock() in psi") # Cc: stable@vger.kernel.org # Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> # Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev> # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux-ld --version # < git log --format=%s --max-count=1 3840cbe24cf060ea05a585ca497814609f5d47d1 # make -s -j 40 ARCH=openrisc O=/kisskb/build/linus_or1ksim_defconfig_or32-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux- or1ksim_defconfig # < make -s -j 40 ARCH=openrisc O=/kisskb/build/linus_or1ksim_defconfig_or32-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux- help # make -s -j 40 ARCH=openrisc O=/kisskb/build/linus_or1ksim_defconfig_or32-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux- olddefconfig # make -s -j 40 ARCH=openrisc O=/kisskb/build/linus_or1ksim_defconfig_or32-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/or1k-linux/bin/or1k-linux- Completed OK # rm -rf /kisskb/build/linus_or1ksim_defconfig_or32-gcc9 # Build took: 0:00:21.673563

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