[Devel] Re: [PATCH] incorrect error handling inside generic_file_direct_write

[Dmitriy Monakhov]

Andrew Morton <akpm at osdl.org> writes:

> On Tue, 12 Dec 2006 16:18:32 +0300
> Dmitriy Monakhov <dmonakhov at sw.ru> wrote:
>
>> >> but according to filemaps locking rules: mm/filemap.c:77
>> >>  ..
>> >>  *  ->i_mutex			(generic_file_buffered_write)
>> >>  *    ->mmap_sem		(fault_in_pages_readable->do_page_fault)
>> >>  ..
>> >> I'm confused a litle bit, where is the truth? 
>> >
>> > xfs_write() calls generic_file_direct_write() without taking i_mutex for
>> > O_DIRECT writes.
>> Yes, but my quastion is about __generic_file_aio_write_nolock().
>> As i understand _nolock sufix means that i_mutex was already locked 
>> by caller, am i right ?
>
> Nope.  It just means that __generic_file_aio_write_nolock() doesn't take
> the lock.  We don't assume or require that the caller took it.  For example
> the raw driver calls generic_file_aio_write_nolock() without taking
> i_mutex.  Raw isn't relevant to the problem (although ocfs2 might be).  But
> we cannot assume that all callers have taken i_mutex, I think.
>
> I guess we can make that a rule (document it, add
> BUG_ON(!mutex_is_locked(..)) if it isn't a blockdev) if needs be.  After
> really checking that this matches reality for all callers.
I've checked generic_file_aio_write_nolock() callers for non blockdev.
Only ocfs2 call it explicitly, and do it under i_mutex.
So we need to do: 
1) Change wrong comments.
2) Add BUG_ON(!mutex_is_locked(..)) for non blkdev.
3) Invoke vmtruncate only for non blkdev.

Signed-off-by: Dmitriy Monakhov <dmonakhov at openvz.org>
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