On Thu, Aug 27, 2015 at 6:48 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Wed, Aug 26, 2015 at 04:16:46PM +0800, Peng Tao wrote:
>> Signed-off-by: Peng Tao <tao.peng@xxxxxxxxxxxxxxx>
>> ---
>> fs/nfs/nfs4file.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 50 insertions(+)
>>
>> diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
>> index dcd39d4..c335cb0 100644
>> --- a/fs/nfs/nfs4file.c
>> +++ b/fs/nfs/nfs4file.c
>> @@ -4,6 +4,7 @@
>> * Copyright (C) 1992 Rick Sladkey
>> */
>> #include <linux/fs.h>
>> +#include <linux/file.h>
>> #include <linux/falloc.h>
>> #include <linux/nfs_fs.h>
>> #include "internal.h"
>> @@ -166,6 +167,54 @@ static long nfs42_fallocate(struct file *filep, int mode, loff_t offset, loff_t
>> return nfs42_proc_deallocate(filep, offset, len);
>> return nfs42_proc_allocate(filep, offset, len);
>> }
>> +
>> +static noinline int
>> +nfs42_file_clone_range(struct file *src_file, struct file *dst_file,
>> + loff_t src_off, size_t dst_off, loff_t count)
>> +{
>> + struct inode *dst_inode = file_inode(dst_file);
>> + struct inode *src_inode = file_inode(src_file);
>> + int ret;
>> +
>> + /* src and dst must be different files */
>> + if (src_inode == dst_inode)
>> + return -EINVAL;
>> +
>> + /* XXX: do we lock at all? what if server needs CB_RECALL_LAYOUT? */
>> + if (dst_inode < src_inode) {
>> + mutex_lock_nested(&dst_inode->i_mutex, I_MUTEX_PARENT);
>> + mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_CHILD);
>> + } else {
>> + mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_PARENT);
>> + mutex_lock_nested(&dst_inode->i_mutex, I_MUTEX_CHILD);
>> + }
>
> Is that safe? Between two operations, the inode code be reclaimed
> and re-instantiated, resulting in the second operation having a
> different locking order for the same files compared to the
> first operation...
Both files are still open so I don't think we need to worry about
inode going away.
>
>> +out_unlock:
>> + if (dst_inode < src_inode) {
>> + mutex_unlock(&src_inode->i_mutex);
>> + mutex_unlock(&dst_inode->i_mutex);
>> + } else {
>> + mutex_unlock(&dst_inode->i_mutex);
>> + mutex_unlock(&src_inode->i_mutex);
>> + }
>
> You don't have to care about lock order on unlock.
Good point!
Thanks,
Tao
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