From nobody Wed Oct 1 23:30:06 2025 Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C13D1F4C90 for ; Sat, 27 Sep 2025 06:53:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.166.71 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758956041; cv=none; b=A+mWQJG2lCwmWXfjPcTP5hnWbCR0ThbbC66YnLWTbCc9olMROfmqzW2+b10Oojes+iySYoOntIiov2yj/2Eb8anTbE5twek044o8PwkNbPagkhdWQJPabTpoaZV2ndEgxg3RsmaUGOSFeTirLwgKIOlU3cAWwUo34fQD90n77g4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758956041; c=relaxed/simple; bh=ews0uAJF2afggW2uR8BzxRbCOlYY1Dqq2Yas/R7b+yo=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=sXGYQeOmvPpMU+d96arxF/OnjftxRXX6s3BvBD+vhLJg1ugNK7FmDn+/4+MczdqwQpOcReHZ4S42XhzjKID0mSsODKlhfwXp/z+owga1iV7f2DgwS1yHGBaqn4HnRAeSvYFK8aA/eP01D/Oiw0AW/hKLy0Zds0HHQGP/yahS2k4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.166.71 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-io1-f71.google.com with SMTP id ca18e2360f4ac-886e347d2afso315433339f.3 for ; Fri, 26 Sep 2025 23:53:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758956037; x=1759560837; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=PYMFv8mT20Sxv6aWto+iww88GaWMZtF+DLGFAgx4DoE=; b=qDhmmMIXyysMCVzrVNvxCmnnqypOepmSDO+86+6Y4idVyWpTJdrewFEPTSYCWMWRb2 f07Iry3rNYU4yEfZYyJn/mEKI5CB88LULcXyK1hDOlGnq+pPS/KNQJX6M//I54zEKRgh jaDaMKpcweUq6pI6cTl22Yk8h4iX2z2P1miyzNbqy7S2qFWkm6nLS00KY9w4wYlsGFBg DlIJnSFMrue/qCwEFzzgYOHLxytW1g/q6xKpoN7oVdbj5kEcj7HqgFl8wGuEk2vxwQUR 4bqj0hJduX+zeMvNOycW5GYASPWJZgGdBcgL6CDf3NFyPKKth25XpLO191D+/La0JrJN f1Fg== X-Gm-Message-State: AOJu0YwMZPWrzBzWlwaM9aK9p37S2vOFs8gAuN18T4RX8lETmRzL/DjD /twzl1BUH8iLYm11PjXjzxDvMd5YOkxtb3vq2zAUPDKwsxo3gQtDimv9jAiwqLiMKtApJMeJrMV IMpKJCMMwva0EmIyGdsqjXYnHyE7dIYoW7b40DVQrJ3H3lSq9EJuRD5+2hxI= X-Google-Smtp-Source: AGHT+IF3Bdn2G7v4qYrTL1q0h5ilPbphsa3JYMoyO3r2EFr2V7vAYhslAHLvMqfEFvrUK3ZXAut61EyvevYFrNNGr1OWFAAduEyE Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6e02:2199:b0:427:db3e:bc10 with SMTP id e9e14a558f8ab-427db3ebe4emr47842395ab.0.1758956037532; Fri, 26 Sep 2025 23:53:57 -0700 (PDT) Date: Fri, 26 Sep 2025 23:53:57 -0700 In-Reply-To: <68cb3c24.050a0220.50883.0029.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <68d78a05.050a0220.25d7ab.0286.GAE@google.com> Subject: Forwarded: [PATCH] bcachefs: Fix deadlock between fallocate and readahead From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] bcachefs: Fix deadlock between fallocate and readahead Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master There is an ABBA deadlock between fallocate and readahead operations: Thread 1 (fallocate): bch2_fallocate_dispatch inode_lock(&inode->v) bch2_pagecache_block_get(inode) // Acquires two_state_lock __bchfs_fallocate bch2_clamp_data_hole bch2_seek_pagecache_hole __filemap_get_folio folio_lock() // BLOCKS - Thread 2 holds it Thread 2 (readahead via copy_file_range): bch2_readahead folio_lock() // Holds page lock __bch2_two_state_lock(&pagecache_lock) // BLOCKS - Thread 1 holds it The issue is that drop_locks_do() only releases btree transaction locks, but Thread 2 is blocked waiting for the two_state_lock (pagecache_block) held by bch2_pagecache_block_get(). Fix by explicitly releasing and re-acquiring the pagecache_block lock around the blocking bch2_clamp_data_hole() call, following the same pattern used in bch2_page_fault(). Force a transaction restart after lock release to ensure consistency. Reported-by: syzbot+cb91f22d8a581fc19edf@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?extid=3Dcb91f22d8a581fc19edf Signed-off-by: Deepanshu Kartikey --- fs/bcachefs/fs-io.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/bcachefs/fs-io.c b/fs/bcachefs/fs-io.c index a233f45875e9..04f76d141b17 100644 --- a/fs/bcachefs/fs-io.c +++ b/fs/bcachefs/fs-io.c @@ -694,13 +694,19 @@ static noinline int __bchfs_fallocate(struct bch_inod= e_info *inode, int mode, &hole_start, &hole_end, opts.data_replicas, true)) { + /* Release pagecache_block to prevent deadlock with readahead */ + bch2_pagecache_block_put(inode); ret =3D drop_locks_do(trans, (bch2_clamp_data_hole(&inode->v, &hole_start, &hole_end, opts.data_replicas, false), 0)); + bch2_pagecache_block_get(inode); if (ret) goto bkey_err; + /* Force transaction restart to revalidate state */ + ret =3D -BCH_ERR_transaction_restart; + goto bkey_err; } bch2_btree_iter_set_pos(trans, &iter, POS(iter.pos.inode, hole_start)); =20 --=20 2.43.0