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Date: Wed, 15 Jan 2020 07:54:06 +0100 From: Christoph Hellwig <hch@....de> To: Matthew Wilcox <willy@...radead.org> Cc: Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, Waiman Long <longman@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-ext4@...r.kernel.org, cluster-devel@...hat.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: RFC: hold i_rwsem until aio completes 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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