The patch titled Subject: CPU hotplug, debug: detect imbalance between get_online_cpus() and put_online_cpus() has been removed from the -mm tree. Its filename was cpu-hotplug-debug-detect-imbalance-between-get_online_cpus-and-put_online_cpus.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: "Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Subject: CPU hotplug, debug: detect imbalance between get_online_cpus() and put_online_cpus() The synchronization between CPU hotplug readers and writers is achieved by means of refcounting, safeguarded by the cpu_hotplug.lock. get_online_cpus() increments the refcount, whereas put_online_cpus() decrements it. If we ever hit an imbalance between the two, we end up compromising the guarantees of the hotplug synchronization i.e, for example, an extra call to put_online_cpus() can end up allowing a hotplug reader to execute concurrently with a hotplug writer. So, add a WARN_ON() in put_online_cpus() to detect such cases where the refcount can go negative, and also attempt to fix it up, so that we can continue to run. Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> Cc: Jiri Kosina <jkosina@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/cpu.c | 4 ++++ 1 file changed, 4 insertions(+) diff -puN kernel/cpu.c~cpu-hotplug-debug-detect-imbalance-between-get_online_cpus-and-put_online_cpus kernel/cpu.c --- a/kernel/cpu.c~cpu-hotplug-debug-detect-imbalance-between-get_online_cpus-and-put_online_cpus +++ a/kernel/cpu.c @@ -80,6 +80,10 @@ void put_online_cpus(void) if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); + + if (WARN_ON(!cpu_hotplug.refcount)) + cpu_hotplug.refcount++; /* try to fix things up */ + if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); _ Patches currently in -mm which might be from srivatsa.bhat@xxxxxxxxxxxxxxxxxx are origin.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html