On Thu, Sep 22, 2016 at 5:49 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> On Thu, Sep 22, 2016 at 10:49 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>> Guys, I just hit a lockdep warning on nesting an mnt_want_write() with
>> this patch
>> because overlay already holds the write lock when getting to ovl_copy_up_data()
>> I don't know how I missed it before.
>>
>> Is it really a problem to nest this lock?
>> Should I factor our another set of _locked helpers from the
>> vfs_{copy,clone}_file_range helpers?
>>
>
> vfs_{copy,clone}_file_range should call sb_start_write() instead of
> mnt_want_write_file(), the checks against FMODE_WRITE + S_ISREG ensure
> that the __mnt_want_write() part is already held on the file.
Wait a minute, I think you got the solution but mixed it up a bit.
IIUC, vfs_{clone,copy} should call __mnt_want_write_file()
instead of mnt_want_write_file(), which will skip sb_start_write()
because file is already open for write and no lockdep warning
and no problem.
Am I missing something?
>
> That still leaves the lockdep warning. We could do
> __vfs_{copy,clone}_file_range() variants without the
> sb_start_write()/sb_end_write() and add the non-underscore variants as
> static inline to fs.h that do call the sb_start/end_write.
>
> Thanks,
> Miklos
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