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SubjectRe: [PATCH] hfsplus: fix concurrent acess of alloc_blocks
On 02/19/2014 12:06 AM, Andrew Morton wrote:
> On Mon, 17 Feb 2014 14:20:47 +0200 Sougata Santra <sougata@tuxera.com> 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:
We can also remove this label ?
> hip->phys_size = inode->i_size;
> _
>



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