6.16-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zhang Yi yi.zhang@huawei.com
commit e2c4c49dee64ca2f42ad2958cbe1805de96b6732 upstream.
After large folios are supported on ext4, writing back a sufficiently large and discontinuous folio may consume a significant number of journal credits, placing considerable strain on the journal. For example, in a 20GB filesystem with 1K block size and 1MB journal size, writing back a 2MB folio could require thousands of credits in the worst-case scenario (when each block is discontinuous and distributed across different block groups), potentially exceeding the journal size. This issue can also occur in ext4_write_begin() and ext4_page_mkwrite() when delalloc is not enabled.
Fix this by ensuring that there are sufficient journal credits before allocating an extent in mpage_map_one_extent() and ext4_block_write_begin(). If there are not enough credits, return -EAGAIN, exit the current mapping loop, restart a new handle and a new transaction, and allocating blocks on this folio again in the next iteration.
Suggested-by: Jan Kara jack@suse.cz Signed-off-by: Zhang Yi yi.zhang@huawei.com Reviewed-by: Jan Kara jack@suse.cz Link: https://patch.msgid.link/20250707140814.542883-6-yi.zhang@huaweicloud.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/inode.c | 41 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 5 deletions(-)
--- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -877,6 +877,26 @@ static void ext4_update_bh_state(struct } while (unlikely(!try_cmpxchg(&bh->b_state, &old_state, new_state))); }
+/* + * Make sure that the current journal transaction has enough credits to map + * one extent. Return -EAGAIN if it cannot extend the current running + * transaction. + */ +static inline int ext4_journal_ensure_extent_credits(handle_t *handle, + struct inode *inode) +{ + int credits; + int ret; + + /* Called from ext4_da_write_begin() which has no handle started? */ + if (!handle) + return 0; + + credits = ext4_chunk_trans_blocks(inode, 1); + ret = __ext4_journal_ensure_credits(handle, credits, credits, 0); + return ret <= 0 ? ret : -EAGAIN; +} + static int _ext4_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh, int flags) { @@ -1175,7 +1195,9 @@ int ext4_block_write_begin(handle_t *han clear_buffer_new(bh); if (!buffer_mapped(bh)) { WARN_ON(bh->b_size != blocksize); - err = get_block(inode, block, bh, 1); + err = ext4_journal_ensure_extent_credits(handle, inode); + if (!err) + err = get_block(inode, block, bh, 1); if (err) break; if (buffer_new(bh)) { @@ -1374,8 +1396,9 @@ retry_journal: ext4_orphan_del(NULL, inode); }
- if (ret == -ENOSPC && - ext4_should_retry_alloc(inode->i_sb, &retries)) + if (ret == -EAGAIN || + (ret == -ENOSPC && + ext4_should_retry_alloc(inode->i_sb, &retries))) goto retry_journal; folio_put(folio); return ret; @@ -2324,6 +2347,11 @@ static int mpage_map_one_extent(handle_t int get_blocks_flags; int err, dioread_nolock;
+ /* Make sure transaction has enough credits for this extent */ + err = ext4_journal_ensure_extent_credits(handle, inode); + if (err < 0) + return err; + trace_ext4_da_write_pages_extent(inode, map); /* * Call ext4_map_blocks() to allocate any delayed allocation blocks, or @@ -2451,7 +2479,7 @@ static int mpage_map_and_submit_extent(h * In the case of ENOSPC, if ext4_count_free_blocks() * is non-zero, a commit should free up blocks. */ - if ((err == -ENOMEM) || + if ((err == -ENOMEM) || (err == -EAGAIN) || (err == -ENOSPC && ext4_count_free_clusters(sb))) { /* * We may have already allocated extents for @@ -2957,6 +2985,8 @@ retry: ret = 0; continue; } + if (ret == -EAGAIN) + ret = 0; /* Fatal error - ENOMEM, EIO... */ if (ret) break; @@ -6751,7 +6781,8 @@ vm_fault_t ext4_page_mkwrite(struct vm_f retry_alloc: /* Start journal and allocate blocks */ err = ext4_block_page_mkwrite(inode, folio, get_block); - if (err == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries)) + if (err == -EAGAIN || + (err == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))) goto retry_alloc; out_ret: ret = vmf_fs_error(err);