From: "Paul E. McKenney" <[email protected]> A long string of get_online_cpus() with each followed by a put_online_cpu() that fails to acquire cpu_hotplug.lock can result in overflow of the cpu_hotplug.puts_pending counter. Although this is perhaps improbably, a system with absolutely no CPU-hotplug operations will have an arbitrarily long time in which this overflow could occur. This commit therefore adds overflow checks to get_online_cpus() and try_get_online_cpus().
Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/cpu.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index 90a3d017b90c..5d220234b3ca 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -86,6 +86,16 @@ static struct { #define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map) #define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map) +static void apply_puts_pending(int max) +{ + int delta; + + if (atomic_read(&cpu_hotplug.puts_pending) >= max) { + delta = atomic_xchg(&cpu_hotplug.puts_pending, 0); + cpu_hotplug.refcount -= delta; + } +} + void get_online_cpus(void) { might_sleep(); @@ -93,6 +103,7 @@ void get_online_cpus(void) return; cpuhp_lock_acquire_read(); mutex_lock(&cpu_hotplug.lock); + apply_puts_pending(65536); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); } @@ -105,6 +116,7 @@ bool try_get_online_cpus(void) if (!mutex_trylock(&cpu_hotplug.lock)) return false; cpuhp_lock_acquire_tryread(); + apply_puts_pending(65536); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); return true; @@ -161,12 +173,7 @@ 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; - } + apply_puts_pending(1); if (likely(!cpu_hotplug.refcount)) break; __set_current_state(TASK_UNINTERRUPTIBLE); -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
