Eric Lee / smarc-ti-linux-kernel

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Commit b2c4623dcd07af4b8ae3b56ae5f879e281c7b4f8

Authored by Paul E. McKenney
1 parent f114040e3e
Exists in ti-lsk-linux-4.1.y and in 10 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04

rcu: More on deadlock between CPU hotplug and expedited grace periods 

Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and
expedited grace periods) was incomplete.  Although it did eliminate
deadlocks involving synchronize_sched_expedited()'s acquisition of
cpu_hotplug.lock via get_online_cpus(), it did nothing about the similar
deadlock involving acquisition of this same lock via put_online_cpus().
This deadlock became apparent with testing involving hibernation.

This commit therefore changes put_online_cpus() acquisition of this lock
to be conditional, and increments a new cpu_hotplug.puts_pending field
in case of acquisition failure.  Then cpu_hotplug_begin() checks for this
new field being non-zero, and applies any changes to cpu_hotplug.refcount.

Reported-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Tested-by: Borislav Petkov <bp@suse.de>

Showing 1 changed file with 13 additions and 1 deletions Side-by-side Diff

... ... @@ -64,6 +64,8 @@
64 64 * an ongoing cpu hotplug operation.
65 65 */
66 66 int refcount;
  67 + /* And allows lockless put_online_cpus(). */
  68 + atomic_t puts_pending;
67 69  
68 70 #ifdef CONFIG_DEBUG_LOCK_ALLOC
69 71 struct lockdep_map dep_map;
... ... @@ -113,7 +115,11 @@
113 115 {
114 116 if (cpu_hotplug.active_writer == current)
115 117 return;
116   - mutex_lock(&cpu_hotplug.lock);
  118 + if (!mutex_trylock(&cpu_hotplug.lock)) {
  119 + atomic_inc(&cpu_hotplug.puts_pending);
  120 + cpuhp_lock_release();
  121 + return;
  122 + }
117 123  
118 124 if (WARN_ON(!cpu_hotplug.refcount))
119 125 cpu_hotplug.refcount++; /* try to fix things up */
... ... @@ -155,6 +161,12 @@
155 161 cpuhp_lock_acquire();
156 162 for (;;) {
157 163 mutex_lock(&cpu_hotplug.lock);
  164 + if (atomic_read(&cpu_hotplug.puts_pending)) {
  165 + int delta;
  166 +
  167 + delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
  168 + cpu_hotplug.refcount -= delta;
  169 + }
158 170 if (likely(!cpu_hotplug.refcount))
159 171 break;
160 172 __set_current_state(TASK_UNINTERRUPTIBLE);