Commit 07a8109d authored by Zhihao Cheng's avatar Zhihao Cheng
Browse files

ext4: Stop trying writing pages if no free blocks generated 

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7CBCS



--------------------------------

Folllowing steps could make ext4_wripages trap into a dead loop:

1. Consume free_clusters until free_clusters > 2 * sbi->s_resv_clusters,
   and free_clusters > EXT4_FREECLUSTERS_WATERMARK.
   // eg. free_clusters = 1422, sbi->s_resv_clusters = 512
   // nr_cpus = 4, EXT4_FREECLUSTERS_WATERMARK = 512
2. umount && mount.  // dirty_clusters = 0
3. Run free_clusters tasks concurrently to write different files, many
   tasks write(appendant) 4K data by da_write method. And each inode will
   consume one data block and one extent block in map_block.
   // There are (free_clusters - EXT4_FREECLUSTERS_WATERMARK = 910)
   // tasks choosing da_write method, left 512 tasks choose write_begin
   // method. If tasks which chooses da_write path run first.
   // dirty_clusters = 910, free_clusters = 1422
   // Tasks which choose write_begin path will get ENOSPC:
   //  free_clusters < (nclusters + dirty_clusters + resv_clusters)
   //  1422 < (1 + 910 + 512)
4. After certain number of map_block iterations in ext4_writepages.
   // free_clusters = 0,
   // dirty_clusters = 910 - (1422 / 2) = 199
5. Delete one 4K file.  // free_clusters = 1
6. ext4_writepages traps into dead loop:
    mpage_map_and_submit_extent
     mpage_map_one_extent // ret = ENOSPC
       ext4_map_blocks -> ext4_ext_map_blocks -> ext4_mb_new_blocks ->
       ext4_claim_free_clusters:
         if (free_clusters >= (nclusters + dirty_clusters)) // false
     if (err == -ENOSPC && ext4_count_free_clusters(sb)) // true
       return err
     *give_up_on_write = true // won't be executed

Fix it by terminating ext4_writepages if no free blocks generated.

Signed-off-by: default avatarZhihao Cheng <chengzhihao1@huawei.com>
parent fc143182

fs/ext4/ext4.h

+1 −0
Original line number Diff line number Diff line
@@ -700,6 +700,7 @@ enum { 
#define EXT4_FREE_BLOCKS_NOFREE_FIRST_CLUSTER	0x0010

#define EXT4_FREE_BLOCKS_NOFREE_LAST_CLUSTER	0x0020

#define EXT4_FREE_BLOCKS_RERESERVE_CLUSTER      0x0040

#define EXT4_FREE_BLOCKS_DONT_WAIT_JOURNAL      0x0080



/*

 * ioctl commands

fs/ext4/extents.c

+3 −1
Original line number Diff line number Diff line
@@ -1294,7 +1294,8 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode, 
			if (!ablocks[i])

				continue;

			ext4_free_blocks(handle, inode, NULL, ablocks[i], 1,

					 EXT4_FREE_BLOCKS_METADATA);

					 EXT4_FREE_BLOCKS_METADATA |

					 EXT4_FREE_BLOCKS_DONT_WAIT_JOURNAL);

		}

	}

	kfree(ablocks);
@@ -4329,6 +4330,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode, 
			ext4_discard_preallocations(inode, 0);

			if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)

				fb_flags = EXT4_FREE_BLOCKS_NO_QUOT_UPDATE;

			fb_flags |= EXT4_FREE_BLOCKS_DONT_WAIT_JOURNAL;

			ext4_free_blocks(handle, inode, NULL, newblock,

					 EXT4_C2B(sbi, allocated_clusters),

					 fb_flags);

fs/ext4/inode.c

+1 −1
Original line number Diff line number Diff line
@@ -2479,7 +2479,7 @@ static int mpage_map_and_submit_extent(handle_t *handle, 
			 * is non-zero, a commit should free up blocks.

			 */

			if ((err == -ENOMEM) ||

			    (err == -ENOSPC && ext4_count_free_clusters(sb))) {

			    (err == -ENOSPC && EXT4_SB(sb)->s_mb_free_pending)) {

				if (progress)

					goto update_disksize;

				return err;

fs/ext4/mballoc.c

+3 −2
Original line number Diff line number Diff line
@@ -5498,8 +5498,9 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode, 
	 * consistency guarantees.

	 */

	if (ext4_handle_valid(handle) &&

	    ((flags & EXT4_FREE_BLOCKS_METADATA) ||

	     !ext4_should_writeback_data(inode))) {

	    (((flags & EXT4_FREE_BLOCKS_METADATA) ||

	     !ext4_should_writeback_data(inode)) &&

	     !(flags & EXT4_FREE_BLOCKS_DONT_WAIT_JOURNAL))) {

		struct ext4_free_data *new_entry;

		/*

		 * We use __GFP_NOFAIL because ext4_free_blocks() is not allowed