On Tue, Oct 28, 2014 at 5:53 PM, Paul E. McKenney <[email protected]> wrote: > 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]>
This patch seems to be missing in the cover letter. Reviewed-by: Pranith Kumar <[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 > -- Pranith -- 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/
