From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f173.google.com (mail-dy1-f173.google.com [74.125.82.173]) (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 9A50A2C027C for ; Thu, 25 Jun 2026 04:09:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782360598; cv=none; b=kAA5onGylh8q1wMHK90/fJKgMbrP4KiuCvzoPZTHHKn7uvh8SILvbtGinFbgazJSiwXrQblwwcORvcdlk5cDyY/mKSVCeQy8VoVh123RFeB3GkmIv/U7w8fsXRPVlZK8LTdX4pTst0JQU8vcR0oIllUS23OdIZIuXyynEWROoTk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782360598; c=relaxed/simple; bh=NVbWg0c0bIjnP7un6x2nk2wfEFF4yb6rURz8f50dCVE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=G++4labAP4nESKs6wopXK1+FQ/p9Fl6yWQueK3itYp8HL2xHQyqO5PwWIM58JWoUWa8zHzXPlfGDDdJZIosyFxL2rP0Ju+okmeBivKwfA47ytvzP/rgDPLiE0NRgpb0LAd51VCJmJ3IQYJIg3D3apLwBgO4c7BYhoM48+LKAEdU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=qB+rysml; arc=none smtp.client-ip=74.125.82.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="qB+rysml" Received: by mail-dy1-f173.google.com with SMTP id 5a478bee46e88-30bc871ecdfso2098574eec.1 for ; Wed, 24 Jun 2026 21:09:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782360597; x=1782965397; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=1cXsNH6ajmormroD9gHzyiRu/jCQ70ZBI9PHsJKrNFU=; b=qB+rysmlebQZcSzW5z5TCXrdz48VGXvnRed0duGQSM8u3a++NZBt819kB8IkIdddYx wBOZDoafHTQ8OIQBBl9Uy8DScYsW2SNcaXVmQgJcGMz2pUv8DM1xajmcLldLHhvrTias s+wZ+oJRW7o75OAeaG1YU+o/bXtiPohH7S8trfzXg/IMVaYl93xNjT2KGmsyE8YOnsl2 zRE/Nf7fCEhl4le+knIJx0jaJgOxPjS5RFwvGrnjd1l4j4KKqxDkh3hfGINmPo0LrcCD 4yBaBOetQTfsVy7IvGHQGD/cRhXmz36dkonbsCvL+HjqPI53CvwIX0qNd9BX4hGgCYqP 3Y9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782360597; x=1782965397; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=1cXsNH6ajmormroD9gHzyiRu/jCQ70ZBI9PHsJKrNFU=; b=HXFrlBcd4dXHUSI4iX9xVHSO8+HxXGRQd9/RPxX4DIq3uAYLNtyiD1o30661AHyDFQ yfBsnHtREm9NYBkKqRkOUKd897+5hLRTy8FZ8E54SeVbL4708YUIlTK/w8yZYRXSbONI zv+Ie4Vdc5U2ma+sKTZ9HQ/wGd6RfhWZyIRWnefsXnHDQU7HSW6Ds7EpFQl9YHAC8RUL PpfIr6rZ1LUeBAksn5NQTjWn++7YG4nu+ECSlaZFb8MNAUbLpT/UpdCMFzJ8xpCt+vqS WEqk5IMXczEITdk3Y7bwRFxI+nB044uxz/FU1IWIA0982CIKrFsuDpkhWTCNkQdIn2xT PUog== X-Forwarded-Encrypted: i=1; AHgh+Rp6vGmKQz1H+/74MQKjAaznzBFUOU0/ULfIf9PcReTOYusiFFQrvFXnPOqFoZGR/Izb6xE3fFGoWxer@vger.kernel.org X-Gm-Message-State: AOJu0YyGQ8jvFJT1aiud3PQWFEJ/Lev/EPh6KVgwSt0aNUtB6mFmwMYw mk+Re4LN5P1bHrsK+CR7o+5GEz4BXon4/fDsRLNR3CFVS37oAzPxItVp X-Gm-Gg: AfdE7ckHeaYPU2OpD8h2Nh/z1BbIMjdOvlUS1/wcqiq6SqnL+NejAavJLFjl0wi8yZM TLHGKKG+RXYwoNXDXjgGk8jle/yDAFia/f4o2UU+7WiPqFCPGbLj+6LMdBIx0TfRcA9+enc59Rq CHLhgcHrUa6DVHn3vddH8HT9os9+vC3t3UnVCbZx86LI95BPO+zmn+Ld2LEuPHRIRJ9iosQsUgA j8ltrtP/GmElmTqdU9JDFt29OBxNNsaJSKEHhC89+dtdDVKtWYF4PtFX85hDxEt9CQ+vilAl7zs //lzbwjwUxBZBGYPGjSe3W72Oc0GQ4K1rFRVQcs7mqQLFTyHr6jRQCoFkaujDurCvPNpLJ4g+/8 dFirr5JwlylQhRXUHdCV/Pps8KBNolnCElXcqracXe0HDsbLK/5b5dy8an3VZhZmvoJziSIorI3 gWMuPkdquSvm8VrDMtsA+yLtILAnUCZt4QzpNJvIx89McLTEVwjcWZwabJqQJJJ0ovxuuDH3Q0i nsUGd/Ss//mDTNcdxkaHc/gh113dwTl5UK+BAIurKRJiA+ERjNwkdODc5J6VPXEzy5mZgysRu0t RXvsBWTuNpKV5AN+GjjXmgg= X-Received: by 2002:a05:7300:8c2c:b0:30c:2af0:1cc with SMTP id 5a478bee46e88-30c84fdf0c5mr1230022eec.34.1782360596583; Wed, 24 Jun 2026 21:09:56 -0700 (PDT) Received: from cs-1047136853211-default.asia-southeast1-b.c.d33bddc1d573818c7-tp.internal (172.19.87.34.bc.googleusercontent.com. [34.87.19.172]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30c7c8b1ae5sm4307151eec.16.2026.06.24.21.09.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jun 2026 21:09:55 -0700 (PDT) From: Aditya Srivastava To: tytso@mit.edu, jack@suse.cz Cc: adilger.kernel@dilger.ca, libaokun@linux.alibaba.com, ritesh.list@gmail.com, yi.zhang@huawei.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Aditya Prakash Srivastava , Colin Ian King Subject: [PATCH v3] ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() Date: Thu, 25 Jun 2026 04:09:35 +0000 Message-ID: <20260625040935.2244-1-aditya.ansh182@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Aditya Prakash Srivastava Syzbot/stress-ng reported an ABBA deadlock in ext4 when exercising concurrent xattr workloads (using the ea_inode mount/format option). The deadlock occurs between the running transaction and the eviction thread: - Task 1 (stress-ng): Holds a reference to a shared mbcache_entry (ce) and calls ext4_xattr_inode_cache_find() -> ext4_iget() to retrieve the corresponding EA inode. Since the EA inode is currently being evicted, ext4_iget() blocks in __wait_on_freeing_inode() waiting for eviction to complete. - Task 2 (eviction thread): Currently evicting the same EA inode in ext4_evict_ea_inode(). It calls mb_cache_entry_wait_unused(oe) which blocks waiting for Task 1 to release the reference to the mbcache_entry. To break this deadlock, implement a new ext4_iget() configuration flag named EXT4_IGET_NOWAIT. When set, perform a non-blocking lookup of the inode via VFS's find_inode_nowait() API. If the inode is currently being evicted (marked with I_FREEING or I_WILL_FREE) or created (I_CREATING), simply skip it (returning -ESTALE) rather than waiting for eviction/creation to complete, breaking the ABBA cycle. If the returned inode is I_NEW, wait for its initialization to clear via wait_on_new_inode(). Finally, standard validation checks (including is_bad_inode, EXT4_EA_INODE_FL, file_acl, and xattr flags) are executed as normal inside check_igot_inode() to fully guarantee VFS-layer safety. In ext4_xattr_inode_cache_find(), invoke ext4_iget() with the new EXT4_IGET_NOWAIT flag to perform the non-blocking cache search. Suggested-by: Jan Kara Reported-by: Colin Ian King Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219283 Fixes: 0a46ef234756 ("ext4: do not create EA inode under buffer lock") Signed-off-by: Aditya Prakash Srivastava --- Changes in v3: - Implement a new ext4_iget() configuration flag named EXT4_IGET_NOWAIT to fully contain the non-blocking lookup and VFS-level validations within inode.c, as requested by Jan Kara. - Skip inodes currently being created (I_CREATING), following Jan Kara's direct feedback. - Remove all open-coded match helpers and VFS state-checks from xattr.c. Changes in v2: - Read inode state locklessly using inode_state_read_once() to resolve a lockdep assertion on cache hit. - Manually restore essential inode/ea_inode validations on the retrieved inode (is_bad_inode, EXT4_EA_INODE_FL, file_acl, and xattr checks) to match VFS safety guarantees and prevent using corrupted/failed inodes. fs/ext4/ext4.h | 3 ++- fs/ext4/inode.c | 41 ++++++++++++++++++++++++++++++++++++++--- fs/ext4/xattr.c | 2 +- 3 files changed, 41 insertions(+), 5 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index b37c136ea3ab..c76dd0bdd3d8 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -3144,7 +3144,8 @@ typedef enum { EXT4_IGET_SPECIAL = 0x0001, /* OK to iget a system inode */ EXT4_IGET_HANDLE = 0x0002, /* Inode # is from a handle */ EXT4_IGET_BAD = 0x0004, /* Allow to iget a bad inode */ - EXT4_IGET_EA_INODE = 0x0008 /* Inode should contain an EA value */ + EXT4_IGET_EA_INODE = 0x0008, /* Inode should contain an EA value */ + EXT4_IGET_NOWAIT = 0x0010 /* Non-blocking lookup (skip if freeing) */ } ext4_iget_flags; extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino, diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index ce99807c5f5b..42a798f333d3 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5270,6 +5270,24 @@ void ext4_set_inode_mapping_order(struct inode *inode) mapping_set_folio_order_range(inode->i_mapping, min_order, max_order); } +static int ext4_iget_match(struct inode *inode, u64 ino, void *data) +{ + bool *is_freeing = data; + + if (inode->i_ino != ino) + return 0; + spin_lock(&inode->i_lock); + if (inode_state_read(inode) & (I_FREEING | I_WILL_FREE | I_CREATING)) { + if (is_freeing) + *is_freeing = true; + spin_unlock(&inode->i_lock); + return -1; + } + __iget(inode); + spin_unlock(&inode->i_lock); + return 1; +} + struct inode *__ext4_iget(struct super_block *sb, unsigned long ino, ext4_iget_flags flags, const char *function, unsigned int line) @@ -5298,9 +5316,26 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino, return ERR_PTR(-EFSCORRUPTED); } - inode = iget_locked(sb, ino); - if (!inode) - return ERR_PTR(-ENOMEM); + if (flags & EXT4_IGET_NOWAIT) { + bool is_freeing = false; + + inode = find_inode_nowait(sb, ino, ext4_iget_match, &is_freeing); + if (is_freeing) + return ERR_PTR(-ESTALE); + if (!inode) { + inode = iget_locked(sb, ino); + if (!inode) + return ERR_PTR(-ENOMEM); + } else { + if (inode_state_read_once(inode) & I_NEW) + wait_on_new_inode(inode); + } + } else { + inode = iget_locked(sb, ino); + if (!inode) + return ERR_PTR(-ENOMEM); + } + if (!(inode_state_read_once(inode) & I_NEW)) { ret = check_igot_inode(inode, flags, function, line); if (ret) { diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 982a1f831e22..21b5670d8503 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1550,7 +1550,7 @@ ext4_xattr_inode_cache_find(struct inode *inode, const void *value, while (ce) { ea_inode = ext4_iget(inode->i_sb, ce->e_value, - EXT4_IGET_EA_INODE); + EXT4_IGET_EA_INODE | EXT4_IGET_NOWAIT); if (IS_ERR(ea_inode)) goto next_entry; ext4_xattr_inode_set_class(ea_inode); -- 2.47.3