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a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1683863099; bh=10DaO0lGOkMyOmCE2RbgGjIgBZk/Z7vqVLApmhZ0NEQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=NzFAgIx9MLyl86zLymF+9gdeksJokq03KCZB+W3c0/G5eT0prnoV+rJYABMx8GfIA sfu3G/VFzm8zI9tMacpB7Al8liEOax1d7TBpAdoStzy7itpLJg0WuSfOekpGO2oPhg exsWdDI7j04QVnlcwOHIX6TDTg7rk+O8T6Idj0/U= Date: Thu, 11 May 2023 20:44:58 -0700 From: Andrew Morton To: Tetsuo Handa Cc: syzbot , syzkaller-bugs@googlegroups.com, Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm Subject: Re: [PATCH] debugobject: don't wake up kswapd from fill_pool() Message-Id: <20230511204458.819f9009d2ef8b46cc163191@linux-foundation.org> In-Reply-To: <6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp> References: <000000000000008ddb05fb5e2576@google.com> <6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4FDAAC0004 X-Stat-Signature: 77a3m9wqdtm39t9b8wpw8sue7n4qibma X-HE-Tag: 1683863101-356072 X-HE-Meta: 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 0+rnMuUP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 11 May 2023 22:47:32 +0900 Tetsuo Handa wrote: > 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. hm. But many GFP_ATOMIC allocation attempts are made with locks held. Why aren't all such callers buggy, by trying to wake kswapd with locks held? What's special about this one? > Also, __GFP_NORETRY is pointless for !__GFP_DIRECT_RECLAIM allocation > > Reported-by: syzbot > Closes: https://syzkaller.appspot.com/bug?extid=fe0c72f0ccbb93786380 > Signed-off-by: Tetsuo Handa > 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; Does this weaken fill_pool()'s allocation attempt more than necessary? We can still pass __GFP_HIGH?