Re: [PATCH 4/6 v7] ext4: Lock i_mutex for punch hole

[Allison Henderson <achender@linux.vnet.ibm.com>]

On 08/30/2011 05:31 PM, Andreas Dilger wrote:
> On 2011-08-30, at 6:28 PM, Allison Henderson wrote:
>> This patch modifies the fallocate routine to lock i_mutex during
>> the punch hole operation.
>>
>> Yongqiang noticed that the vfs layer locks i_mutex for truncate,
>> but not fallocate, so the fallocate routine will need to take
>> care of locking i_mutex.  Otherwise a page may be mapped after
>> punch hole has released the pages, but before i_data_sem is
>> locked to release the blocks in the extent tree.
>
> If the VFS is locking i_mutex for truncate, shouldn't the locking for
> fallocate() also be done in the VFS?

Alrighty, I will do some poking around with this idea first.  I dont 
know if other files systems are already locking i_mutex during 
fallocate, and it may be the case that not all filesystems need i_mutex 
locked for fallocate.  So I'll do a little research first, but I will 
post back with what I find.  Thx!

Allison Henderson

>
>> Signed-off-by: Allison Henderson<achender@linux.vnet.ibm.com>
>> ---
>> :100644 100644 9124cd2... 007fb08... M	fs/ext4/extents.c
>> fs/ext4/extents.c |   10 +++++++---
>> 1 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index 9124cd2..007fb08 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -3774,8 +3774,13 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>> 	if (mode&  ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
>> 		return -EOPNOTSUPP;
>>
>> -	if (mode&  FALLOC_FL_PUNCH_HOLE)
>> -		return ext4_punch_hole(file, offset, len);
>> +	mutex_lock(&inode->i_mutex);
>> +
>> +	if (mode&  FALLOC_FL_PUNCH_HOLE) {
>> +		ret = ext4_punch_hole(file, offset, len);
>> +		mutex_unlock(&inode->i_mutex);
>> +		return ret;	
>> +	}
>>
>> 	trace_ext4_fallocate_enter(inode, offset, len, mode);
>> 	map.m_lblk = offset>>  blkbits;
>> @@ -3789,7 +3794,6 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>> 	 * credits to insert 1 extent into extent tree
>> 	 */
>> 	credits = ext4_chunk_trans_blocks(inode, max_blocks);
>> -	mutex_lock(&inode->i_mutex);
>> 	ret = inode_newsize_ok(inode, (len + offset));
>> 	if (ret) {
>> 		mutex_unlock(&inode->i_mutex);
>> --
>> 1.7.1
>>
>> --
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>
>
> Cheers, Andreas
>
>
>
>
>