+ mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch added to -mm tree

+ mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/slab.c: protect cache_reap() against CPU and memory hot plug operations
has been added to the -mm tree.  Its filename is
     mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch

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------------------------------------------------------
From: Laurent Dufour <ldufour@linux.ibm.com>
Subject: mm/slab.c: protect cache_reap() against CPU and memory hot plug operations

95402b382901 ("cpu-hotplug: replace per-subsystem mutexes with
get_online_cpus()") remove the CPU_LOCK_ACQUIRE operation which was use to
grap the cache_chain_mutex lock which was protecting cache_reap() against
CPU hot plug operations.

Later 18004c5d4084 ("mm, sl[aou]b: Use a common mutex definition") changed
cache_chain_mutex to slab_mutex but this didn't help fixing the missing
the cache_reap() protection against CPU hot plug operations.

Here we are stopping the per cpu worker while holding the slab_mutex to
ensure that cache_reap() is not running in our back and will not be
triggered anymore for this cpu.

This patch fixes that race leading to SLAB's data corruption when CPU
hotplug are triggered.  We hit it while doing partition migration on
PowerVM leading to CPU reconfiguration through the CPU hotplug mechanism.

This fix is covering kernel containing to the commit 6731d4f12315 ("slab:
Convert to hotplug state machine"), ie 4.9.1, earlier kernel needs a
slightly different patch.

Link: http://lkml.kernel.org/r/20190311191701.24325-1-ldufour@linux.ibm.com
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/slab.c~mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations
+++ a/mm/slab.c
@@ -1103,6 +1103,7 @@ static int slab_online_cpu(unsigned int
 
 static int slab_offline_cpu(unsigned int cpu)
 {
+	mutex_lock(&slab_mutex);
 	/*
 	 * Shutdown cache reaper. Note that the slab_mutex is held so
 	 * that if cache_reap() is invoked it cannot do anything
@@ -1112,6 +1113,7 @@ static int slab_offline_cpu(unsigned int
 	cancel_delayed_work_sync(&per_cpu(slab_reap_work, cpu));
 	/* Now the cache_reaper is guaranteed to be not running. */
 	per_cpu(slab_reap_work, cpu).work.func = NULL;
+	mutex_unlock(&slab_mutex);
 	return 0;
 }
 
_

Patches currently in -mm which might be from ldufour@linux.ibm.com are

mm-slab-protect-cache_reap-against-cpu-and-memory-hot-plug-operations.patch