Messages in this thread | | | Date | Wed, 15 Jan 2020 07:54:06 +0100 | From | Christoph Hellwig <> | Subject | Re: RFC: hold i_rwsem until aio completes |
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On Tue, Jan 14, 2020 at 10:47:07AM -0800, Matthew Wilcox wrote: > It would be helpful if we could also use the same lockdep logic > for PageLocked. Again, it's a case where returning to userspace with > PageLock held is fine, because we're expecting an interrupt to come in > and drop the lock for us.
Yes, this is a very typical pattern for I/O. Besides the page and buffer head bit locks it also applies to the semaphore in the xfs_buf structure and probably various other places that currently used hand crafted or legacy locking primitives to escape lockdep.
> Perhaps the right answer is, from lockdep's point of view, to mark the > lock as being released at the point where we submit the I/O. Then > in the completion path release the lock without telling lockdep we > released it.
That is similar to what the fsfreeze code does, but I don't think it is very optimal, as misses to track any dependencies after I/O submission, and at least some of the completions paths do take locks. But it might be a start.
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