ext4: fast commit: make s_fc_lock reclaim-safe

s_fc_lock can be acquired from inode eviction and thus is
reclaim unsafe. Since the fast commit path holds s_fc_lock while writing
the commit log, allocations under the lock can enter reclaim and invert
the lock order with fs_reclaim. Add ext4_fc_lock()/ext4_fc_unlock()
helpers which acquire s_fc_lock under memalloc_nofs_save()/restore()
context and use them everywhere so allocations under the lock cannot
recurse into filesystem reclaim.

Fixes: 6593714d67ba ("ext4: hold s_fc_lock while during fast commit")
Signed-off-by: Li Chen <me@linux.beauty>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260106120621.440126-1-me@linux.beauty
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3b54542083054f0623f5c755390bffba0f4be65d..9610602fe37b358eece4858cd5acdfecdf48070f 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1788,6 +1788,10 @@ struct ext4_sb_info {
         * Main fast commit lock. This lock protects accesses to the
         * following fields:
         * ei->i_fc_list, s_fc_dentry_q, s_fc_q, s_fc_bytes, s_fc_bh.
+        *
+        * s_fc_lock can be taken from reclaim context (inode eviction) and is
+        * thus reclaim unsafe. Use ext4_fc_lock()/ext4_fc_unlock() helpers
+        * when acquiring / releasing the lock.
         */
        struct mutex s_fc_lock;
        struct buffer_head *s_fc_bh;
@@ -1832,6 +1836,18 @@ static inline void ext4_writepages_up_write(struct super_block *sb, int ctx)
        percpu_up_write(&EXT4_SB(sb)->s_writepages_rwsem);
 }
 
+static inline int ext4_fc_lock(struct super_block *sb)
+{
+       mutex_lock(&EXT4_SB(sb)->s_fc_lock);
+       return memalloc_nofs_save();
+}
+
+static inline void ext4_fc_unlock(struct super_block *sb, int ctx)
+{
+       memalloc_nofs_restore(ctx);
+       mutex_unlock(&EXT4_SB(sb)->s_fc_lock);
+}
+
 static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 {
        return ino == EXT4_ROOT_INO ||

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 0ef2154a2b1f55fbc15e17a554e7599d986d8065..f575751f1cae430eead31afa4f7d03ade1099d4a 100644 (file)
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -231,16 +231,16 @@ static bool ext4_fc_disabled(struct super_block *sb)
 void ext4_fc_del(struct inode *inode)
 {
        struct ext4_inode_info *ei = EXT4_I(inode);
-       struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_fc_dentry_update *fc_dentry;
        wait_queue_head_t *wq;
+       int alloc_ctx;
 
        if (ext4_fc_disabled(inode->i_sb))
                return;
 
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(inode->i_sb);
        if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
-               mutex_unlock(&sbi->s_fc_lock);
+               ext4_fc_unlock(inode->i_sb, alloc_ctx);
                return;
        }
 
@@ -275,9 +275,9 @@ void ext4_fc_del(struct inode *inode)
 #endif
                prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
                if (ext4_test_inode_state(inode, EXT4_STATE_FC_FLUSHING_DATA)) {
-                       mutex_unlock(&sbi->s_fc_lock);
+                       ext4_fc_unlock(inode->i_sb, alloc_ctx);
                        schedule();
-                       mutex_lock(&sbi->s_fc_lock);
+                       alloc_ctx = ext4_fc_lock(inode->i_sb);
                }
                finish_wait(wq, &wait.wq_entry);
        }
@@ -288,7 +288,7 @@ void ext4_fc_del(struct inode *inode)
         * dentry create references, since it is not needed to log it anyways.
         */
        if (list_empty(&ei->i_fc_dilist)) {
-               mutex_unlock(&sbi->s_fc_lock);
+               ext4_fc_unlock(inode->i_sb, alloc_ctx);
                return;
        }
 
@@ -298,7 +298,7 @@ void ext4_fc_del(struct inode *inode)
        list_del_init(&fc_dentry->fcd_dilist);
 
        WARN_ON(!list_empty(&ei->i_fc_dilist));
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(inode->i_sb, alloc_ctx);
 
        release_dentry_name_snapshot(&fc_dentry->fcd_name);
        kmem_cache_free(ext4_fc_dentry_cachep, fc_dentry);
@@ -315,6 +315,7 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason, handle_t *handl
        tid_t tid;
        bool has_transaction = true;
        bool is_ineligible;
+       int alloc_ctx;
 
        if (ext4_fc_disabled(sb))
                return;
@@ -329,12 +330,12 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason, handle_t *handl
                        has_transaction = false;
                read_unlock(&sbi->s_journal->j_state_lock);
        }
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        is_ineligible = ext4_test_mount_flag(sb, EXT4_MF_FC_INELIGIBLE);
        if (has_transaction && (!is_ineligible || tid_gt(tid, sbi->s_fc_ineligible_tid)))
                sbi->s_fc_ineligible_tid = tid;
        ext4_set_mount_flag(sb, EXT4_MF_FC_INELIGIBLE);
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
        WARN_ON(reason >= EXT4_FC_REASON_MAX);
        sbi->s_fc_stats.fc_ineligible_reason_count[reason]++;
 }
@@ -358,6 +359,7 @@ static int ext4_fc_track_template(
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        tid_t tid = 0;
+       int alloc_ctx;
        int ret;
 
        tid = handle->h_transaction->t_tid;
@@ -373,14 +375,14 @@ static int ext4_fc_track_template(
        if (!enqueue)
                return ret;
 
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(inode->i_sb);
        if (list_empty(&EXT4_I(inode)->i_fc_list))
                list_add_tail(&EXT4_I(inode)->i_fc_list,
                                (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
                                 sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) ?
                                &sbi->s_fc_q[FC_Q_STAGING] :
                                &sbi->s_fc_q[FC_Q_MAIN]);
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(inode->i_sb, alloc_ctx);
 
        return ret;
 }
@@ -402,6 +404,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
        struct inode *dir = dentry->d_parent->d_inode;
        struct super_block *sb = inode->i_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
+       int alloc_ctx;
 
        spin_unlock(&ei->i_fc_lock);
 
@@ -425,7 +428,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
        take_dentry_name_snapshot(&node->fcd_name, dentry);
        INIT_LIST_HEAD(&node->fcd_dilist);
        INIT_LIST_HEAD(&node->fcd_list);
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        if (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
                sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING)
                list_add_tail(&node->fcd_list,
@@ -446,7 +449,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
                WARN_ON(!list_empty(&ei->i_fc_dilist));
                list_add_tail(&node->fcd_dilist, &ei->i_fc_dilist);
        }
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
        spin_lock(&ei->i_fc_lock);
 
        return 0;
@@ -1046,18 +1049,19 @@ static int ext4_fc_perform_commit(journal_t *journal)
        struct blk_plug plug;
        int ret = 0;
        u32 crc = 0;
+       int alloc_ctx;
 
        /*
         * Step 1: Mark all inodes on s_fc_q[MAIN] with
         * EXT4_STATE_FC_FLUSHING_DATA. This prevents these inodes from being
         * freed until the data flush is over.
         */
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
                ext4_set_inode_state(&iter->vfs_inode,
                                     EXT4_STATE_FC_FLUSHING_DATA);
        }
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
 
        /* Step 2: Flush data for all the eligible inodes. */
        ret = ext4_fc_flush_data(journal);
@@ -1067,7 +1071,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
         * any error from step 2. This ensures that waiters waiting on
         * EXT4_STATE_FC_FLUSHING_DATA can resume.
         */
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
                ext4_clear_inode_state(&iter->vfs_inode,
                                       EXT4_STATE_FC_FLUSHING_DATA);
@@ -1084,7 +1088,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
         * prepare_to_wait() in ext4_fc_del().
         */
        smp_mb();
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
 
        /*
         * If we encountered error in Step 2, return it now after clearing
@@ -1101,12 +1105,12 @@ static int ext4_fc_perform_commit(journal_t *journal)
         * previous handles are now drained. We now mark the inodes on the
         * commit queue as being committed.
         */
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
                ext4_set_inode_state(&iter->vfs_inode,
                                     EXT4_STATE_FC_COMMITTING);
        }
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
        jbd2_journal_unlock_updates(journal);
 
        /*
@@ -1117,6 +1121,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
                blkdev_issue_flush(journal->j_fs_dev);
 
        blk_start_plug(&plug);
+       alloc_ctx = ext4_fc_lock(sb);
        /* Step 6: Write fast commit blocks to disk. */
        if (sbi->s_fc_bytes == 0) {
                /*
@@ -1134,7 +1139,6 @@ static int ext4_fc_perform_commit(journal_t *journal)
        }
 
        /* Step 6.2: Now write all the dentry updates. */
-       mutex_lock(&sbi->s_fc_lock);
        ret = ext4_fc_commit_dentry_updates(journal, &crc);
        if (ret)
                goto out;
@@ -1156,7 +1160,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
        ret = ext4_fc_write_tail(sb, crc);
 
 out:
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
        blk_finish_plug(&plug);
        return ret;
 }
@@ -1290,6 +1294,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_inode_info *ei;
        struct ext4_fc_dentry_update *fc_dentry;
+       int alloc_ctx;
 
        if (full && sbi->s_fc_bh)
                sbi->s_fc_bh = NULL;
@@ -1297,7 +1302,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
        trace_ext4_fc_cleanup(journal, full, tid);
        jbd2_fc_release_bufs(journal);
 
-       mutex_lock(&sbi->s_fc_lock);
+       alloc_ctx = ext4_fc_lock(sb);
        while (!list_empty(&sbi->s_fc_q[FC_Q_MAIN])) {
                ei = list_first_entry(&sbi->s_fc_q[FC_Q_MAIN],
                                        struct ext4_inode_info,
@@ -1356,7 +1361,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
 
        if (full)
                sbi->s_fc_bytes = 0;
-       mutex_unlock(&sbi->s_fc_lock);
+       ext4_fc_unlock(sb, alloc_ctx);
        trace_ext4_fc_stats(sb);
 }