Re: Commit 35ce7f29a breaks hibernation for XPS 13

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Oct 24, 2014 at 12:08:15PM -0400, Eric B Munson wrote:
> Paul,
> 
> As of 3.18-rc1 I can no longer hibernate my Dell XPS-13.  Bisect points
> the finger at 35ce7f29a.  A revert of that commit confirms, I can once
> again hibernate my machine without it.
> 
> When the hibernation fails I see this in dmesg:
> [   37.953313] PM: Syncing filesystems ... done.
> [   37.963694] Freezing user space processes ... (elapsed 0.001 seconds) done.
> [   37.965297] PM: Marking nosave pages: [mem 0x00000000-0x00000fff]
> [   37.965299] PM: Marking nosave pages: [mem 0x00058000-0x00058fff]
> [   37.965301] PM: Marking nosave pages: [mem 0x0009d000-0x000fffff]
> [   37.965304] PM: Marking nosave pages: [mem 0xc496a000-0xc4b6bfff]
> [   37.965315] PM: Marking nosave pages: [mem 0xdadb7000-0xdcffefff]
> [   37.965479] PM: Marking nosave pages: [mem 0xdd000000-0xffffffff]
> [   37.966000] PM: Basic memory bitmaps created
> [   37.966046] PM: Preallocating image memory... done (allocated 181989 pages)
> [   38.141524] PM: Allocated 727956 kbytes in 0.17 seconds (4282.09 MB/s)
> [   38.141525] Freezing remaining freezable tasks ... 
> [   58.151863] Freezing of tasks failed after 20.004 seconds (0 tasks refusing to freeze, wq_busy=1):
> [   58.151894] 
> [   58.151896] Restarting kernel threads ... done.
> [   58.181915] PM: Basic memory bitmaps freed
> [   58.181917] Restarting tasks ... done.
> 
> 
> I am not sure what else I can provide that might be useful, but I did
> see the thread on net-dev about this same commit.  Please CC me on any
> fixes and I will be happy to test.

Thank you for the bug report!

Does the following patch help?

							Thanx, Paul

------------------------------------------------------------------------

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>

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 356450f09c1f..90a3d017b90c 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -64,6 +64,8 @@ static struct {
 	 * an ongoing cpu hotplug operation.
 	 */
 	int refcount;
+	/* And allows lockless put_online_cpus(). */
+	atomic_t puts_pending;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
@@ -113,7 +115,11 @@ void put_online_cpus(void)
 {
 	if (cpu_hotplug.active_writer == current)
 		return;
-	mutex_lock(&cpu_hotplug.lock);
+	if (!mutex_trylock(&cpu_hotplug.lock)) {
+		atomic_inc(&cpu_hotplug.puts_pending);
+		cpuhp_lock_release();
+		return;
+	}
 
 	if (WARN_ON(!cpu_hotplug.refcount))
 		cpu_hotplug.refcount++; /* try to fix things up */
@@ -155,6 +161,12 @@ void cpu_hotplug_begin(void)
 	cpuhp_lock_acquire();
 	for (;;) {
 		mutex_lock(&cpu_hotplug.lock);
+		if (atomic_read(&cpu_hotplug.puts_pending)) {
+			int delta;
+
+			delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
+			cpu_hotplug.refcount -= delta;
+		}
 		if (likely(!cpu_hotplug.refcount))
 			break;
 		__set_current_state(TASK_UNINTERRUPTIBLE);