Patch "mm/kasan: don't reduce quarantine in atomic contexts" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

mm/kasan: don't reduce quarantine in atomic contexts

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-kasan-don-t-reduce-quarantine-in-atomic-contexts.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrey Ryabinin <[email protected]>
Date: Tue, 2 Aug 2016 14:02:43 -0700
Subject: mm/kasan: don't reduce quarantine in atomic contexts

From: Andrey Ryabinin <[email protected]>

commit 4b3ec5a3f4b1d5c9d64b9ab704042400d050d432 upstream.

Currently we call quarantine_reduce() for ___GFP_KSWAPD_RECLAIM (implied by __GFP_RECLAIM) allocation. So, basically we call it on almost every allocation. quarantine_reduce() sometimes is heavy operation, and calling it with disabled interrupts may trigger hard LOCKUP:

NMI watchdog: Watchdog detected hard LOCKUP on cpu 2irq event stamp: 1411258

 Call Trace:
  <NMI>   dump_stack+0x68/0x96
   watchdog_overflow_callback+0x15b/0x190
   __perf_event_overflow+0x1b1/0x540
   perf_event_overflow+0x14/0x20
   intel_pmu_handle_irq+0x36a/0xad0
   perf_event_nmi_handler+0x2c/0x50
   nmi_handle+0x128/0x480
   default_do_nmi+0xb2/0x210
   do_nmi+0x1aa/0x220
   end_repeat_nmi+0x1a/0x1e
  <<EOE>>   __kernel_text_address+0x86/0xb0
   print_context_stack+0x7b/0x100
   dump_trace+0x12b/0x350
   save_stack_trace+0x2b/0x50
   set_track+0x83/0x140
   free_debug_processing+0x1aa/0x420
   __slab_free+0x1d6/0x2e0
   ___cache_free+0xb6/0xd0
   qlist_free_all+0x83/0x100
   quarantine_reduce+0x177/0x1b0
   kasan_kmalloc+0xf3/0x100

Reduce the quarantine_reduce iff direct reclaim is allowed.

---
 mm/kasan/kasan.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -562,7 +562,7 @@ void kasan_kmalloc(struct kmem_cache *ca
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
-	if (flags & __GFP_RECLAIM)
+	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();
 
 	if (unlikely(object == NULL))

@@ -595,7 +595,7 @@ void kasan_kmalloc_large(const void *ptr
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
-	if (flags & __GFP_RECLAIM)
+	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();
 
 	if (unlikely(ptr == NULL))

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/mm-kasan-don-t-reduce-quarantine-in-atomic-contexts.patch queue-4.7/kasan-avoid-overflowing-quarantine-size-on-low-memory-systems.patch