mm: memcontrol: fix false-positive VM_BUG_ON() on -rt

On -rt, the VM_BUG_ON(!irqs_disabled()) triggers inside the memcg
swapout path because the spin_lock_irq(&mapping->tree_lock) in the
caller doesn't actually disable the hardware interrupts - which is fine,
because on -rt the tophalves run in process context and so we are still
safe from preemption while updating the statistics.

Remove the VM_BUG_ON() but keep the comment of what we rely on.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Clark Williams <williams@redhat.com>
Cc: Fernando Lopez-Lezcano <nando@ccrma.Stanford.EDU>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9da23a7ec4c00b04ced3e349e8dc8a5c6ca016b3..a04225d372ba3ab77516b970c10135b19def3ac4 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5835,9 +5835,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
        if (!mem_cgroup_is_root(memcg))
                page_counter_uncharge(&memcg->memory, 1);
 
-       /* XXX: caller holds IRQ-safe mapping->tree_lock */
-       VM_BUG_ON(!irqs_disabled());
-
+       /* Caller disabled preemption with mapping->tree_lock */
        mem_cgroup_charge_statistics(memcg, page, -1);
        memcg_check_events(memcg, page);
 }