From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CF91B1A6827; Mon, 4 May 2026 14:18:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777904313; cv=none; b=Ymk1EUwxYyzQD3MGr5AsIoqEiI3OlfaKRfAJZGi22HTL6Go4ivVbUK6fH0d2pno3tG1upl/3AfuKaYnTJvd3GiCA1/eonrNwMVNPOxz4tQphDoRofkNWcwaveIzLy1/fI0dDgXqlhPWFQ6GursFOvr2ZNmO0NQlOplf9Z+YGA/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777904313; c=relaxed/simple; bh=x8y7Kc+TT486OKW9qGpQWU8/n0xwiyQIy/znZejkcgY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LKzCZpHVBcSHofUJx9JmovphAKg1561RxhNUhbUajx5/hVb6NhDE7hVLjznEEIxQ2aid9qGg18BhPjRm1p87KsNtU+HrCHmiCifI4wG9ZMiWlEYrOE8nk1g1M8rX6LUT6Kj9zwl45PyUnNx22N8FQB1tOEclkWHjGNebCySWK/A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=1iTZHyC+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="1iTZHyC+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64F61C2BCB8; Mon, 4 May 2026 14:18:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777904313; bh=x8y7Kc+TT486OKW9qGpQWU8/n0xwiyQIy/znZejkcgY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1iTZHyC+1rOF9MiN1QKLbPJ91qdbHIO5o91UmmPssO9kJc85Qd+f3P149413s+oXx 88VzMvm7bcu2SRoxZfVYVRxlNsd6rC+rhqkqtm/SnnBwiPsQMK8A4dwRNL30xIwhJx OiII+cqEJOP2GjrIpjlCkMlc54gI24UDqQyjlfR0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Max Kellermann , Viacheslav Dubeyko , Ilya Dryomov Subject: [PATCH 6.18 234/275] ceph: only d_add() negative dentries when they are unhashed Date: Mon, 4 May 2026 15:52:54 +0200 Message-ID: <20260504135151.745023114@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260504135142.929052779@linuxfoundation.org> References: <20260504135142.929052779@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Max Kellermann commit 803447f93d75ab6e40c85e6d12b5630d281d70d6 upstream. Ceph can call d_add(dentry, NULL) on a negative dentry that is already present in the primary dcache hash. In the current VFS that is not safe. d_add() goes through __d_add() to __d_rehash(), which unconditionally reinserts dentry->d_hash into the hlist_bl bucket. If the dentry is already hashed, reinserting the same node can corrupt the bucket, including creating a self-loop. Once that happens, __d_lookup() can spin forever in the hlist_bl walk, typically looping only on the d_name.hash mismatch check and eventually triggering RCU stall reports like this one: rcu: INFO: rcu_sched self-detected stall on CPU rcu: 87-....: (2100 ticks this GP) idle=3a4c/1/0x4000000000000000 softirq=25003319/25003319 fqs=829 rcu: (t=2101 jiffies g=79058445 q=698988 ncpus=192) CPU: 87 UID: 2952868916 PID: 3933303 Comm: php-cgi8.3 Not tainted 6.18.17-i1-amd #950 NONE Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.6 09/22/2023 RIP: 0010:__d_lookup+0x46/0xb0 Code: c1 e8 07 48 8d 04 c2 48 8b 00 49 89 fc 49 89 f5 48 89 c3 48 83 e3 fe 48 83 f8 01 77 0f eb 2d 0f 1f 44 00 00 48 8b 1b 48 85 db <74> 20 39 6b 18 75 f3 48 8d 7b 78 e8 ba 85 d0 00 4c 39 63 10 74 1f RSP: 0018:ff745a70c8253898 EFLAGS: 00000282 RAX: ff26e470054cb208 RBX: ff26e470054cb208 RCX: 000000006e958966 RDX: ff26e48267340000 RSI: ff745a70c82539b0 RDI: ff26e458f74655c0 RBP: 000000006e958966 R08: 0000000000000180 R09: 9cd08d909b919a89 R10: ff26e458f74655c0 R11: 0000000000000000 R12: ff26e458f74655c0 R13: ff745a70c82539b0 R14: d0d0d0d0d0d0d0d0 R15: 2f2f2f2f2f2f2f2f FS: 00007f5770896980(0000) GS:ff26e482c5d88000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f5764de50c0 CR3: 000000a72abb5001 CR4: 0000000000771ef0 PKRU: 55555554 Call Trace: lookup_fast+0x9f/0x100 walk_component+0x1f/0x150 link_path_walk+0x20e/0x3d0 path_lookupat+0x68/0x180 filename_lookup+0xdc/0x1e0 vfs_statx+0x6c/0x140 vfs_fstatat+0x67/0xa0 __do_sys_newfstatat+0x24/0x60 do_syscall_64+0x6a/0x230 entry_SYSCALL_64_after_hwframe+0x76/0x7e This is reachable with reused cached negative dentries. A Ceph lookup or atomic_open can be handed a negative dentry that is already hashed, and fs/ceph/dir.c then hits one of two paths that incorrectly assume "negative" also means "unhashed": - ceph_finish_lookup(): MDS reply is -ENOENT with no trace -> d_add(dentry, NULL) - ceph_lookup(): local ENOENT fast path for a complete directory with shared caps -> d_add(dentry, NULL) Both paths can therefore re-add an already-hashed negative dentry. Ceph already uses the correct pattern elsewhere: ceph_fill_trace() only calls d_add(dn, NULL) for a negative null-dentry reply when d_unhashed(dn) is true. Fix both fs/ceph/dir.c sites the same way: only call d_add() for a negative dentry when it is actually unhashed. If the negative dentry is already hashed, leave it in place and reuse it as-is. This preserves the existing behavior for unhashed dentries while avoiding d_hash list corruption for reused hashed negatives. Cc: stable@vger.kernel.org Fixes: 2817b000b02c ("ceph: directory operations") Signed-off-by: Max Kellermann Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Greg Kroah-Hartman --- fs/ceph/dir.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/fs/ceph/dir.c +++ b/fs/ceph/dir.c @@ -769,7 +769,8 @@ struct dentry *ceph_finish_lookup(struct d_drop(dentry); err = -ENOENT; } else { - d_add(dentry, NULL); + if (d_unhashed(dentry)) + d_add(dentry, NULL); } } } @@ -840,7 +841,8 @@ static struct dentry *ceph_lookup(struct spin_unlock(&ci->i_ceph_lock); doutc(cl, " dir %llx.%llx complete, -ENOENT\n", ceph_vinop(dir)); - d_add(dentry, NULL); + if (d_unhashed(dentry)) + d_add(dentry, NULL); di->lease_shared_gen = atomic_read(&ci->i_shared_gen); return NULL; }