linux-kernel - [PATCH] debugobject: don't wake up kswapd from fill

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Message-ID: <6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp>
Date:   Thu, 11 May 2023 22:47:32 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     syzbot <syzbot+fe0c72f0ccbb93786380@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com, Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: [PATCH] debugobject: don't wake up kswapd from fill_pool()

syzbot is reporting lockdep warning in fill_pool(), for GFP_ATOMIC is
(__GFP_HIGH | __GFP_KSWAPD_RECLAIM) which wakes up kswapd.
Since fill_pool() might be called with arbitrary locks held,
fill_pool() should not assume that holding pgdat->kswapd_wait is safe.

Also, __GFP_NORETRY is pointless for !__GFP_DIRECT_RECLAIM allocation.

Reported-by: syzbot <syzbot+fe0c72f0ccbb93786380@...kaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=fe0c72f0ccbb93786380
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Fixes: 3ac7fe5a4aab ("infrastructure to debug (dynamic) objects")
---
 lib/debugobjects.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 003edc5ebd67..986adca357b4 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -126,7 +126,7 @@ static const char *obj_states[ODEBUG_STATE_MAX] = {
 
 static void fill_pool(void)
 {
-	gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
+	gfp_t gfp = __GFP_HIGH | __GFP_NOWARN;
 	struct debug_obj *obj;
 	unsigned long flags;
 
-- 
2.18.4