linux-kernel - [tip: core/debugobjects] debugobjects: Don't wake up kswapd from fill

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Message-ID: <168476016890.404.6911447269153588182.tip-bot2@tip-bot2>
Date:   Mon, 22 May 2023 12:56:08 -0000
From:   "tip-bot2 for Tetsuo Handa" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     syzbot <syzbot+fe0c72f0ccbb93786380@...kaller.appspotmail.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/debugobjects] debugobjects: Don't wake up kswapd from fill_pool()

The following commit has been merged into the core/debugobjects branch of tip:

Commit-ID:     eb799279fb1f9c63c520fe8c1c41cb9154252db6
Gitweb:        https://git.kernel.org/tip/eb799279fb1f9c63c520fe8c1c41cb9154252db6
Author:        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
AuthorDate:    Thu, 11 May 2023 22:47:32 +09:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 22 May 2023 14:52:58 +02:00

debugobjects: Don't wake up kswapd from fill_pool()

syzbot is reporting a lockdep warning in fill_pool() because the allocation
from debugobjects is using GFP_ATOMIC, which is (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)
and therefore tries to wake up kswapd, which acquires kswapd_wait::lock.

Since fill_pool() might be called with arbitrary locks held, fill_pool()
should not assume that acquiring kswapd_wait::lock is safe.

Use __GFP_HIGH instead and remove __GFP_NORETRY as it is pointless for
!__GFP_DIRECT_RECLAIM allocation.

Fixes: 3ac7fe5a4aab ("infrastructure to debug (dynamic) objects")
Reported-by: syzbot <syzbot+fe0c72f0ccbb93786380@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp
Closes: https://syzkaller.appspot.com/bug?extid=fe0c72f0ccbb93786380
---
 lib/debugobjects.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 826c617..984985c 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;