[PATCH] lib/stackdepot: stackdepot: don't use __GFP_KSWAPD_RECLAIM from __stack_depot_save() if atomic context

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

syzbot is reporting lockdep warning in __stack_depot_save(), for
wakeup_kswapd() from wake_all_kswapds() from __alloc_pages_slowpath()
calls wakeup_kcompactd() when __GFP_KSWAPD_RECLAIM is set and
__GFP_DIRECT_RECLAIM is not set (i.e. GFP_ATOMIC).

Since __stack_depot_save() might be called with arbitrary locks held,
__stack_depot_save() should not wake kswapd which in turn wakes kcompactd.

Reported-by: syzbot <syzbot+ece2915262061d6e0ac1@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=ece2915262061d6e0ac1
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: cd11016e5f52 ("mm, kasan: stackdepot implementation. Enable stackdepot for SLAB")
---
 lib/stackdepot.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 2f5aa851834e..5c331a80b87a 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -405,7 +405,10 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		 * contexts and I/O.
 		 */
 		alloc_flags &= ~GFP_ZONEMASK;
-		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
+		if (!(alloc_flags & __GFP_DIRECT_RECLAIM))
+			alloc_flags &= __GFP_HIGH;
+		else
+			alloc_flags &= GFP_KERNEL;
 		alloc_flags |= __GFP_NOWARN;
 		page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
 		if (page)
-- 
2.18.4