Re: [PATCH 6/6] ovl: concurrent copy up of regular files

[Amir Goldstein <amir73il@gmail.com>]

On Mon, Jan 16, 2017 at 1:05 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Sun, Jan 15, 2017 at 2:57 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>> Now that copy up of regular file is done using O_TMPFILE,
>> we don't need to hold rename_lock throughout copy up.
>>
>> Use the copy up waitqueue to synchronize concurrent copy up
>> of the same file. Different regular files can be copied up
>> concurrently.
>>
>> The upper dir inode_lock is taken instead of rename_lock,
>> because it is needed for lookup and later for linking the
>> temp file, but it is released while copying up data.
>>
>> Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
>> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>> ---
>>  fs/overlayfs/copy_up.c | 23 +++++++++++++++++++++++
>>  1 file changed, 23 insertions(+)
>>
>> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
>> index d3b6c15..ddf5e2d 100644
>> --- a/fs/overlayfs/copy_up.c
>> +++ b/fs/overlayfs/copy_up.c
>> @@ -291,7 +291,14 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
>>                 BUG_ON(upperpath.dentry != NULL);
>>                 upperpath.dentry = temp;
>>
>> +               if (tmpfile)
>> +                       inode_unlock(udir);
>> +
>>                 err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
>> +
>> +               if (tmpfile)
>> +                       inode_lock_nested(udir, I_MUTEX_PARENT);
>> +
>>                 if (err)
>>                         goto out_cleanup;
>>         }
>> @@ -371,6 +378,19 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
>>                         return PTR_ERR(link);
>>         }
>>
>> +       if (tmpfile) {
>> +               err = ovl_copy_up_start(dentry);
>> +               /* err < 0: interrupted, err > 0: raced with another copy-up */
>> +               if (unlikely(err)) {
>> +                       pr_debug("ovl_copy_up_start(%pd2) = %i\n", dentry, err);
>> +                       if (err > 0)
>> +                               err = 0;
>> +                       goto out_done;
>> +               }
>> +               /* lock_rename/unlock_rename will lock/unlock only upperdir */
>> +               workdir = upperdir;
>
> Unnecessary obfuscation.   Just do lock_inode(); ovl_copy_up_locked();
> unlokc_inode();.
>

upperdir still needs to be locked for ovl_set_timestamps(), so I can do:

+                    inode_lock_nested(udir, I_MUTEX_PARENT)
+           } else {
>>         if (lock_rename(workdir, upperdir) != NULL) {
>>                 pr_err("overlayfs: failed to lock workdir+upperdir\n");
...
>>  out_unlock:
+             if (tmpfile)
+                     inode_unlock(udir);
+             else
>>         unlock_rename(workdir, upperdir);
>> +       if (tmpfile)
>> +               ovl_copy_up_end(dentry);
>> +out_done:
>>         do_delayed_call(&done);
>>
>>         return err;
>> --
>> 2.7.4
>>