# git rev-parse -q --verify f9bc9bbe8afdf83412728f0b464979a72a3b9ec2^{commit} f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 already have revision, skipping fetch # git checkout -q -f -B kisskb f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # git clean -qxdf # < git log -1 # commit f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # Author: Nicholas Piggin # Date: Mon Oct 16 22:43:00 2023 +1000 # # powerpc/qspinlock: Fix stale propagated yield_cpu # # yield_cpu is a sample of a preempted lock holder that gets propagated # back through the queue. Queued waiters use this to yield to the # preempted lock holder without continually sampling the lock word (which # would defeat the purpose of MCS queueing by bouncing the cache line). # # The problem is that yield_cpu can become stale. It can take some time to # be passed down the chain, and if any queued waiter gets preempted then # it will cease to propagate the yield_cpu to later waiters. # # This can result in yielding to a CPU that no longer holds the lock, # which is bad, but particularly if it is currently in H_CEDE (idle), # then it appears to be preempted and some hypervisors (PowerVM) can # cause very long H_CONFER latencies waiting for H_CEDE wakeup. This # results in latency spikes and hard lockups on oversubscribed # partitions with lock contention. # # This is a minimal fix. Before yielding to yield_cpu, sample the lock # word to confirm yield_cpu is still the owner, and bail out of it is not. # # Thanks to a bunch of people who reported this and tracked down the # exact problem using tracepoints and dispatch trace logs. # # Fixes: 28db61e207ea ("powerpc/qspinlock: allow propagation of yield CPU down the queue") # Cc: stable@vger.kernel.org # v6.2+ # Reported-by: Srikar Dronamraju # Reported-by: Laurent Dufour # Reported-by: Shrikanth Hegde # Debugged-by: "Nysal Jan K.A" # Signed-off-by: Nicholas Piggin # Tested-by: Shrikanth Hegde # Signed-off-by: Michael Ellerman # Link: https://msgid.link/20231016124305.139923-2-npiggin@gmail.com # < /opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux-ld --version # < git log --format=%s --max-count=1 f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 # make -s -j 24 ARCH=s390 O=/kisskb/build/powerpc-fixes_defconfig_s390x-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux- defconfig # Added to kconfig CONFIG_DEBUG_INFO_BTF=n # Added to kconfig # < make -s -j 24 ARCH=s390 O=/kisskb/build/powerpc-fixes_defconfig_s390x-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux- help # make -s -j 24 ARCH=s390 O=/kisskb/build/powerpc-fixes_defconfig_s390x-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux- olddefconfig .config:3702:warning: override: reassigning to symbol DEBUG_INFO_BTF # make -s -j 24 ARCH=s390 O=/kisskb/build/powerpc-fixes_defconfig_s390x-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/s390-linux/bin/s390-linux- Completed OK # rm -rf /kisskb/build/powerpc-fixes_defconfig_s390x-gcc12 # Build took: 0:09:04.821299