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[35.240.129.69]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30c1bd8d6edsm15415857eec.14.2026.06.23.02.59.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jun 2026 02:59:30 -0700 (PDT) From: Aditya Srivastava To: tytso@mit.edu Cc: jack@suse.cz, 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 v2] ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() Date: Tue, 23 Jun 2026 09:59:11 +0000 Message-ID: <20260623095911.2372-1-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, perform a non-blocking lookup of the EA inode using VFS's find_inode_nowait() API. If the EA inode is currently being evicted (marked with I_FREEING or I_WILL_FREE), simply skip it (treat as a cache miss) rather than waiting for eviction to complete. If the returned inode is found to be I_NEW, wait for its initialization to clear using wait_on_new_inode(). This deadlock was made much easier to hit after commit 0a46ef234756 ("ext4: do not create EA inode under buffer lock") which removed synchronization on the buffer lock. 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 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/xattr.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 982a1f831e22..ef13e7a76153 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1523,6 +1523,20 @@ static struct inode *ext4_xattr_inode_create(handle_t *handle, return ea_inode; } +static int ext4_xattr_inode_match(struct inode *inode, u64 ino, void *data) +{ + if (inode->i_ino != ino) + return 0; + spin_lock(&inode->i_lock); + if (inode_state_read(inode) & (I_FREEING | I_WILL_FREE)) { + spin_unlock(&inode->i_lock); + return 0; + } + __iget(inode); + spin_unlock(&inode->i_lock); + return 1; +} + static struct inode * ext4_xattr_inode_cache_find(struct inode *inode, const void *value, size_t value_len, u32 hash) @@ -1549,10 +1563,19 @@ 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); - if (IS_ERR(ea_inode)) + ea_inode = find_inode_nowait(inode->i_sb, ce->e_value, + ext4_xattr_inode_match, NULL); + if (!ea_inode) goto next_entry; + if (inode_state_read_once(ea_inode) & I_NEW) + wait_on_new_inode(ea_inode); + if (is_bad_inode(ea_inode) || + !(EXT4_I(ea_inode)->i_flags & EXT4_EA_INODE_FL) || + ext4_test_inode_state(ea_inode, EXT4_STATE_XATTR) || + EXT4_I(ea_inode)->i_file_acl) { + iput(ea_inode); + goto next_entry; + } ext4_xattr_inode_set_class(ea_inode); if (i_size_read(ea_inode) == value_len && !ext4_xattr_inode_read(ea_inode, ea_data, value_len) && -- 2.47.3