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 00CEB3F2101; Tue, 13 Oct 2026 12:23:01 +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=1791894182; cv=none; b=tGu3zOaXDxYoiwgnyNhiyDB2ysfmUa2jHgVjoE7+tdsl8Xj2Ry7ve2LMwLgBHPcRb93QIowQPRHxQ8Iu2JUJios0zzH3o5/H/29sUvkIt69ybriplxKcS14W7j+2VjH2wJnd07448G60HlHO/EjoUPGxr+SW5yPghvN84NOtnU8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791894182; c=relaxed/simple; bh=EbPWDrDHG3aX+gdWskCxWyIHp69FWfIHEA3vQCfo5Fk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qk+XRQzIe7r0+BF72LG08KKr03VzR1bUubNnsDlBl+xNkvXfVmQ+6+giMNNSLSEth6Dzrsh3Wcun+j+POQruiHT4SgfUzWBNuo+qhINo39nfB+QeOSir7wq/zNfKYyIzyABJJOimFmi3slRRQmw6ChjXosQaLRbArqriM7A48LA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Q9Z/moiC; 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="Q9Z/moiC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 829D61F000FF; Tue, 13 Oct 2026 12:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791894180; bh=GSRl874Xq1ETfAdniQM6cV1U57S3NjRsCa/NAP3UM0E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Q9Z/moiCWK7oNxXYinVLap3hdaJmlrMy2QHrqYcxDyfcAV3NMtcV0gfFJxJ2m9Dbd GexDfZ6CCDTirMDK3OnwMd3wW2TAvrg1tv68yeQvV6PPaPj0j6jFsHsstrxxVzBr0c SXPi4i3TQcMAeWKZM9mFKAt42SPybmkKzzCqYJI4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , Colin Ian King , Aditya Prakash Srivastava , Theodore Tso , Sasha Levin Subject: [PATCH 6.18 473/621] ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() Date: Tue, 13 Oct 2026 13:37:48 +0200 Message-ID: <20261013112932.058980699@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@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: Aditya Prakash Srivastava [ Upstream commit 03438084a7b8621fb5c762dd3d04cff5f2630fb2 ] 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), or if it is not present in the VFS inode cache (cache miss), simply skip it (returning -ENOENT) rather than waiting for eviction/creation to complete, breaking the ABBA cycle. Since we return -ENOENT immediately on a cache miss, we never attempt to allocate a new inode or call iget_locked(), completely eliminating any TOCTOU race window. If the returned inode is I_NEW, wait for its initialization to clear via wait_on_new_inode(). If initialization fails and the inode is unhashed during wait_on_new_inode() waking up (e.g., due to an I/O read error in another thread), safely drop the reference and return -ENOENT. This unhashed check is executed unconditionally on all cache-hit pathways to properly handle concurrent initialization failures. 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 Tested-by: Colin Ian King Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260626054821.1729-1-aditya.ansh182@gmail.com Signed-off-by: Theodore Ts'o Signed-off-by: Sasha Levin --- fs/ext4/ext4.h | 3 ++- fs/ext4/inode.c | 35 ++++++++++++++++++++++++++++++++--- fs/ext4/xattr.c | 2 +- 3 files changed, 35 insertions(+), 5 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 996ffdc2dd13d..da6428312c36b 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -3081,7 +3081,8 @@ 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 d2977c560c96b..bbc437be5e63b 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5210,6 +5210,20 @@ void ext4_set_inode_mapping_order(struct inode *inode) EXT4_MAX_PAGECACHE_ORDER(inode)); } +static int ext4_iget_match(struct inode *inode, unsigned long ino, void *data) +{ + if (inode->i_ino != ino) + return 0; + spin_lock(&inode->i_lock); + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_CREATING)) { + 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) @@ -5238,9 +5252,24 @@ 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) { + inode = find_inode_nowait(sb, ino, ext4_iget_match, NULL); + if (!inode) + return ERR_PTR(-ENOENT); + + if (inode->i_state & I_NEW) + wait_on_inode(inode); + + if (unlikely(inode_unhashed(inode))) { + iput(inode); + return ERR_PTR(-ENOENT); + } + } else { + inode = iget_locked(sb, ino); + if (!inode) + return ERR_PTR(-ENOMEM); + } + if (!(inode->i_state & 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 02095ca17be0f..789e7087a5490 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); -- 2.53.0