From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [91.216.245.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 627BA148838; Sun, 11 Aug 2024 13:24:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.216.245.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723382663; cv=none; b=mrGzcZ+/wMMgg43q1HdjlmBGsTAFQC/oDWo/NEKEt72E9Lew4p3CeOcaf57y1WVOQ7DSzX7GTEqiM2+sb2DFLWUMVuSxqPT8+NV7HQSy0Ukhgx7cM8FvOhx7XDHdDpYfTrhi5k67uNLPhk8TA5ABzi2eRhJZ3VZ3pPWY2W7luCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723382663; c=relaxed/simple; bh=Po5/mFOf0/VTScGzn6+mtQuzX/UGKG4Vw71o8feai/U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rywU/UX41czih6GDcckmzd8V/ZFUrY8ApPPhpGarGLxLhvRrtUhWvtT4No2Hc8JrY9v0WjDADAkprOkU2aF//Z6ePQ738n4dX+iTtqlx6KvfYq6TcoYga5yLrKNwXTHCTyKvI8M0jnEveUpnNpp2VniP8n65bvsc52yMJbRDZuA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de; spf=pass smtp.mailfrom=strlen.de; arc=none smtp.client-ip=91.216.245.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=strlen.de Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1sd8YN-0004rw-GL; Sun, 11 Aug 2024 15:24:11 +0200 Date: Sun, 11 Aug 2024 15:24:11 +0200 From: Florian Westphal To: Kuniyuki Iwashima Cc: syzbot+8ea26396ff85d23a8929@syzkaller.appspotmail.com, davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [net?] WARNING: refcount bug in inet_twsk_kill Message-ID: <20240811132411.GB13736@breakpoint.cc> References: <0000000000003a5292061f5e4e19@google.com> <20240811022903.49188-1-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240811022903.49188-1-kuniyu@amazon.com> User-Agent: Mutt/1.10.1 (2018-07-13) Kuniyuki Iwashima wrote: > From: syzbot > Date: Sat, 10 Aug 2024 18:29:20 -0700 > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 33e02dc69afb Merge tag 'sound-6.10-rc1' of git://git.kerne.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=117f3182980000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=25544a2faf4bae65 > > dashboard link: https://syzkaller.appspot.com/bug?extid=8ea26396ff85d23a8929 > > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-33e02dc6.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/573c88ac3233/vmlinux-33e02dc6.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/760a52b9a00a/bzImage-33e02dc6.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+8ea26396ff85d23a8929@syzkaller.appspotmail.com > > > > ------------[ cut here ]------------ > > refcount_t: decrement hit 0; leaking memory. > > WARNING: CPU: 3 PID: 1396 at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31 > > Eric, this is the weird report I was talking about at netdevconf :) > > It seems refcount_dec(&tw->tw_dr->tw_refcount) is somehow done earlier > than refcount_inc(). > > I started to see the same splat at a very low rate after consuming > commit b334b924c9b7 ("net: tcp/dccp: prepare for tw_timer un-pinning"). I think I see why. The reported splat is without this above commit. But from backtrace we entered here: if (net->ipv4.tcp_death_row.hashinfo->pernet) { /* Even if tw_refcount == 1, we must clean up kernel reqsk */ inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); } else if (!purged_once) { --------------> inet_twsk_purge(&tcp_hashinfo); // THIS purged_once = true; > The commit a bit deferred refcount_inc(tw_refcount) after the hash dance, > so twsk is now visible before tw_dr->tw_refcount is incremented. > > I came up with the diff below but was suspecting a bug in another place, > possibly QEMU, so I haven't posted the diff officially. > > refcount_inc() was actually deferred, but it's still under an ehash lock, but different struct inet_hashinfo, so the locks don't help :/