From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3FFCA46D57E; Tue, 21 Jul 2026 15:44:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784648644; cv=none; b=nIFpyGp68aBsJlneTldGdtN0aarG6/O2cMAnD8Y+eNwcyWaznlExjaT/JrHG7vkqcmrFHgUs6bhxTwSCuFUqc5NmeSfDE19eoID2YGYL+CUM82jl3JBSvGGgbjJzSCJK8uSWaHlpQyqZW8XlHOIDpdVwS+BdSZQapD/sFTTPnI4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784648644; c=relaxed/simple; bh=HgOifuwG6vaINmKGfUrNgmJICZ3IsvnDSORb8bsLuf0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kuNF58uQb2rJLjgU3g3zpmv+Tu6orCrKcYtGPOn/Osp3LNWeGXrGVNiDbBrTCNMUh/3jgq757A8cRYNlSOoUOcFv+evGWfTABoAlKqGyRBn/waEm9XuUKB1EUTnNdBz95cHUYBif6iU8yzUDPFEpl2/v36OzULP4JDXSSzSAwWk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=xzRzoLe+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="xzRzoLe+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87B461F000E9; Tue, 21 Jul 2026 15:44:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784648642; bh=adzqu1U8KVUAKR2FCvc0ufM8nqu7by5XRG4A29WvGjA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=xzRzoLe+fgskFI0dlsve891miFdyOtYWHxdSsXyu6amN54xyLFEForzDDvuGRIwpa p/XAJzfsFFxhEvbkkrm13O4Z4N8kTHIzRftMDFYV4lpYUZTRNmxxzXpefC7ZQJDn2J XWDF8TN2ymHYEUF36dXsXiEuV8TgzoESQ4AWijsA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+0dfe499ea713e0a15bec@syzkaller.appspotmail.com, Conor Kotwasinski , Tejun Heo , Sasha Levin Subject: [PATCH 7.1 0278/2077] kernfs: fix suspicious RCU usage in kernfs_put() Date: Tue, 21 Jul 2026 16:59:11 +0200 Message-ID: <20260721152559.240222672@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152552.646164743@linuxfoundation.org> References: <20260721152552.646164743@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 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Conor Kotwasinski [ Upstream commit 0fdde3f2aeadcf8d090ee3edee0aad73fb91f690 ] Commit 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.") converted the WARN_ONCE() in kernfs_put() to read kn->name and parent->name via rcu_dereference(), but kernfs_put() has callers that hold neither kernfs_rwsem nor the RCU read lock. The inode eviction path driven by memory reclaim is one such case: kernfs_put+0x53/0x60 fs/kernfs/dir.c:602 evict+0x3c2/0xad0 fs/inode.c:846 iput_final fs/inode.c:1966 [inline] iput.part.0+0x605/0xf50 fs/inode.c:2015 iput+0x35/0x40 fs/inode.c:1981 dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467 __dentry_kill+0x1d0/0x600 fs/dcache.c:670 shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174 prune_dcache_sb+0xea/0x150 fs/dcache.c:1256 super_cache_scan+0x328/0x550 fs/super.c:223 ... kswapd+0x556/0xba0 mm/vmscan.c:7343 lockdep complains with "suspicious RCU usage" whenever the WARN fires from such a context. Wrap the rcu_dereference() calls in an RCU read-side critical section. Gate on the active-ref check so the lock is only taken when the WARN is about to fire. Note that this does not address the underlying imbalance in kn->active that triggers the WARN. Fixes: 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.") Reported-by: syzbot+0dfe499ea713e0a15bec@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=0dfe499ea713e0a15bec Signed-off-by: Conor Kotwasinski Acked-by: Tejun Heo Link: https://patch.msgid.link/20260416134315.1474726-1-conorkotwasinski2024@u.northwestern.edu Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- fs/kernfs/dir.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 4f9ade82b08abd..e88b71607f1e51 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -597,10 +597,13 @@ void kernfs_put(struct kernfs_node *kn) */ parent = kernfs_parent(kn); - WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS, - "kernfs_put: %s/%s: released with incorrect active_ref %d\n", - parent ? rcu_dereference(parent->name) : "", - rcu_dereference(kn->name), atomic_read(&kn->active)); + if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS) { + guard(rcu)(); + WARN_ONCE(1, + "kernfs_put: %s/%s: released with incorrect active_ref %d\n", + parent ? rcu_dereference(parent->name) : "", + rcu_dereference(kn->name), atomic_read(&kn->active)); + } if (kernfs_type(kn) == KERNFS_LINK) kernfs_put(kn->symlink.target_kn); -- 2.53.0