From: Jan Kara Date: Fri, 20 Mar 2026 09:04:29 +0000 (+0100) Subject: ext4: fix deadlock on inode reallocation X-Git-Tag: v7.0-rc6~12^2~4 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0c90eed1b95335eba4f546e6742a8e4503d79349;p=thirdparty%2Flinux.git ext4: fix deadlock on inode reallocation Currently there is a race in ext4 when reallocating freed inode resulting in a deadlock: Task1 Task2 ext4_evict_inode() handle = ext4_journal_start(); ... if (IS_SYNC(inode)) handle->h_sync = 1; ext4_free_inode() ext4_new_inode() handle = ext4_journal_start() finds the bit in inode bitmap already clear insert_inode_locked() waits for inode to be removed from the hash. ext4_journal_stop(handle) jbd2_journal_stop(handle) jbd2_log_wait_commit(journal, tid); - deadlocks waiting for transaction handle Task2 holds Fix the problem by removing inode from the hash already in ext4_clear_inode() by which time all IO for the inode is done so reuse is already fine but we are still before possibly blocking on transaction commit. Reported-by: "Lai, Yi" Link: https://lore.kernel.org/all/abNvb2PcrKj1FBeC@ly-workstation Fixes: 88ec797c4680 ("fs: make insert_inode_locked() wait for inode destruction") CC: stable@vger.kernel.org Signed-off-by: Jan Kara Link: https://patch.msgid.link/20260320090428.24899-2-jack@suse.cz Signed-off-by: Theodore Ts'o Cc: stable@kernel.org --- diff --git a/fs/ext4/super.c b/fs/ext4/super.c index cb69a9b38b7c..a34efb44e73d 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1523,6 +1523,27 @@ void ext4_clear_inode(struct inode *inode) invalidate_inode_buffers(inode); clear_inode(inode); ext4_discard_preallocations(inode); + /* + * We must remove the inode from the hash before ext4_free_inode() + * clears the bit in inode bitmap as otherwise another process reusing + * the inode will block in insert_inode_hash() waiting for inode + * eviction to complete while holding transaction handle open, but + * ext4_evict_inode() still running for that inode could block waiting + * for transaction commit if the inode is marked as IS_SYNC => deadlock. + * + * Removing the inode from the hash here is safe. There are two cases + * to consider: + * 1) The inode still has references to it (i_nlink > 0). In that case + * we are keeping the inode and once we remove the inode from the hash, + * iget() can create the new inode structure for the same inode number + * and we are fine with that as all IO on behalf of the inode is + * finished. + * 2) We are deleting the inode (i_nlink == 0). In that case inode + * number cannot be reused until ext4_free_inode() clears the bit in + * the inode bitmap, at which point all IO is done and reuse is fine + * again. + */ + remove_inode_hash(inode); ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS); dquot_drop(inode); if (EXT4_I(inode)->jinode) {