On Tue, 12 Dec 2006 16:18:32 +0300
Dmitriy Monakhov <[email protected]> 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.
It's important, too - if we have an unprotected i_size_write() then the
seqlock can get out of sync due to a race and then i_size_read() locks up
the kernel.
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