6.5-stable patches

added patches:
	powerpc-qspinlock-fix-stale-propagated-yield_cpu.patch

diff --git a/queue-6.5/powerpc-qspinlock-fix-stale-propagated-yield_cpu.patch b/queue-6.5/powerpc-qspinlock-fix-stale-propagated-yield_cpu.patch
new file mode 100644 (file)
index 0000000..aa16f7a
--- /dev/null
+++ b/queue-6.5/powerpc-qspinlock-fix-stale-propagated-yield_cpu.patch
@@ -0,0 +1,63 @@
+From f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 Mon Sep 17 00:00:00 2001
+From: Nicholas Piggin <npiggin@gmail.com>
+Date: Mon, 16 Oct 2023 22:43:00 +1000
+Subject: powerpc/qspinlock: Fix stale propagated yield_cpu
+
+From: Nicholas Piggin <npiggin@gmail.com>
+
+commit f9bc9bbe8afdf83412728f0b464979a72a3b9ec2 upstream.
+
+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 <srikar@linux.vnet.ibm.com>
+Reported-by: Laurent Dufour <ldufour@linux.ibm.com>
+Reported-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
+Debugged-by: "Nysal Jan K.A" <nysal@linux.ibm.com>
+Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
+Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
+Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
+Link: https://msgid.link/20231016124305.139923-2-npiggin@gmail.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/powerpc/lib/qspinlock.c | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
+index 253620979d0c..6dd2f46bd3ef 100644
+--- a/arch/powerpc/lib/qspinlock.c
++++ b/arch/powerpc/lib/qspinlock.c
+@@ -406,6 +406,9 @@ static __always_inline bool yield_to_prev(struct qspinlock *lock, struct qnode *
+       if ((yield_count & 1) == 0)
+               goto yield_prev; /* owner vcpu is running */
+ 
++      if (get_owner_cpu(READ_ONCE(lock->val)) != yield_cpu)
++              goto yield_prev; /* re-sample lock owner */
++
+       spin_end();
+ 
+       preempted = true;
+-- 
+2.42.0
+

diff --git a/queue-6.5/series b/queue-6.5/series
index e3c5bd0f2616c1489dbc359c3e7e95b4c426218e..a34eedfa03d7d11a4405df06daf0a5769e1e975b 100644 (file)
--- a/queue-6.5/series
+++ b/queue-6.5/series
@@ -224,3 +224,4 @@ drm-panel-move-aux-b116xw03-out-of-panel-edp-back-to.patch
 drm-i915-cx0-only-clear-set-the-pipe-reset-bit-of-th.patch
 drm-amdgpu-fix-possible-null-pointer-dereference.patch
 powerpc-mm-allow-arch_force_max_order-up-to-12.patch
+powerpc-qspinlock-fix-stale-propagated-yield_cpu.patch