On Mon, 17 Feb 2014 14:20:47 +0200 Sougata Santra <sougata@xxxxxxxxxx> wrote:
>
> Concurrent access to alloc_blocks in hfsplus_inode_info is
> protected by extents_lock mutex. This patch fixes two
> instances where alloc_blocks modification was not protected
> with this lock. This fixes possible allocation bitmap
> corruption in race conditions while extending and truncating
> files.
>
> ...
>
> --- a/fs/hfsplus/extents.c
> +++ b/fs/hfsplus/extents.c
> @@ -498,11 +498,13 @@ int hfsplus_file_extend(struct inode *inode)
> goto insert_extent;
> }
> out:
> - mutex_unlock(&hip->extents_lock);
> if (!res) {
> hip->alloc_blocks += len;
> + mutex_unlock(&hip->extents_lock);
> hfsplus_mark_inode_dirty(inode, HFSPLUS_I_ALLOC_DIRTY);
> + return 0;
> }
> + mutex_unlock(&hip->extents_lock);
> return res;
>
This looks OK.
> @@ -592,9 +594,9 @@ void hfsplus_file_truncate(struct inode *inode)
> hfs_brec_remove(&fd);
> }
> hfs_find_exit(&fd);
> - mutex_unlock(&hip->extents_lock);
>
> hip->alloc_blocks = blk_cnt;
> + mutex_unlock(&hip->extents_lock);
> out:
> hip->phys_size = inode->i_size;
> hip->fs_blocks = (inode->i_size + sb->s_blocksize - 1) >>
But this does not. To provide locking for
hfsplus_inode_info.alloc_blocks, we must take the lock *before* taking
a local copy of ->alloc_blocks.
Please review:
--- a/fs/hfsplus/extents.c~hfsplus-fix-concurrent-acess-of-alloc_blocks-fix
+++ a/fs/hfsplus/extents.c
@@ -556,11 +556,13 @@ void hfsplus_file_truncate(struct inode
blk_cnt = (inode->i_size + HFSPLUS_SB(sb)->alloc_blksz - 1) >>
HFSPLUS_SB(sb)->alloc_blksz_shift;
+
+ mutex_lock(&hip->extents_lock);
+
alloc_cnt = hip->alloc_blocks;
if (blk_cnt == alloc_cnt)
- goto out;
+ goto out_unlock;
- mutex_lock(&hip->extents_lock);
res = hfs_find_init(HFSPLUS_SB(sb)->ext_tree, &fd);
if (res) {
mutex_unlock(&hip->extents_lock);
@@ -594,6 +596,7 @@ void hfsplus_file_truncate(struct inode
hfs_find_exit(&fd);
hip->alloc_blocks = blk_cnt;
+out_unlock:
mutex_unlock(&hip->extents_lock);
out:
hip->phys_size = inode->i_size;
_
--
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