68 lines
2.2 KiB
Diff
68 lines
2.2 KiB
Diff
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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Date: Wed, 22 Oct 2014 10:00:05 -0700
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Subject: [PATCH] rcu: More on deadlock between CPU hotplug and expedited grace
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periods
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Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and
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expedited grace periods) was incomplete. Although it did eliminate
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deadlocks involving synchronize_sched_expedited()'s acquisition of
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cpu_hotplug.lock via get_online_cpus(), it did nothing about the similar
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deadlock involving acquisition of this same lock via put_online_cpus().
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This deadlock became apparent with testing involving hibernation.
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This commit therefore changes put_online_cpus() acquisition of this lock
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to be conditional, and increments a new cpu_hotplug.puts_pending field
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in case of acquisition failure. Then cpu_hotplug_begin() checks for this
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new field being non-zero, and applies any changes to cpu_hotplug.refcount.
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Reported-by: Jiri Kosina <jkosina@suse.cz>
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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Tested-by: Jiri Kosina <jkosina@suse.cz>
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Tested-by: Borislav Petkov <bp@suse.de>
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---
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kernel/cpu.c | 14 +++++++++++++-
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1 file changed, 13 insertions(+), 1 deletion(-)
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diff --git a/kernel/cpu.c b/kernel/cpu.c
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index 356450f09c1f..90a3d017b90c 100644
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--- a/kernel/cpu.c
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+++ b/kernel/cpu.c
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@@ -64,6 +64,8 @@ static struct {
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* an ongoing cpu hotplug operation.
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*/
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int refcount;
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+ /* And allows lockless put_online_cpus(). */
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+ atomic_t puts_pending;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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@@ -113,7 +115,11 @@ void put_online_cpus(void)
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{
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if (cpu_hotplug.active_writer == current)
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return;
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- mutex_lock(&cpu_hotplug.lock);
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+ if (!mutex_trylock(&cpu_hotplug.lock)) {
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+ atomic_inc(&cpu_hotplug.puts_pending);
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+ cpuhp_lock_release();
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+ return;
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+ }
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if (WARN_ON(!cpu_hotplug.refcount))
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cpu_hotplug.refcount++; /* try to fix things up */
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@@ -155,6 +161,12 @@ void cpu_hotplug_begin(void)
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cpuhp_lock_acquire();
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for (;;) {
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mutex_lock(&cpu_hotplug.lock);
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+ if (atomic_read(&cpu_hotplug.puts_pending)) {
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+ int delta;
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+
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+ delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
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+ cpu_hotplug.refcount -= delta;
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+ }
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if (likely(!cpu_hotplug.refcount))
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break;
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__set_current_state(TASK_UNINTERRUPTIBLE);
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--
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1.9.3
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