On Wed, 3 Mar 2021 13:26:40 +0000 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > But here's the thing ... invalidate_mapping_pages() doesn't > ClearPageUptodate. The only places where we ClearPageUptodate is on an > I/O error. yup. > So ... as far as I can tell, the only way to hit this is: > > - Get an I/O error during the wait > - Have another thread cause the page to be removed from the page cache > (eg do direct I/O to the file) before this thread is run. > > and the consequence to this change is that we have another attempt to > read the page instead of returning an error immediately. I'm OK with > that unintentional change, although I think the previous behaviour was > also perfectly acceptable (after all, there was an I/O error while trying > to read this page). > > Delving into the linux-fullhistory tree, this code was introduced by ... > > commit 56f0d5fe6851037214a041a5cb4fc66199256544 > Author: Andrew Morton <akpm@xxxxxxxx> > Date: Fri Jan 7 22:03:01 2005 -0800 > > [PATCH] readpage-vs-invalidate fix > > A while ago we merged a patch which tried to solve a problem wherein a > concurrent read() and invalidate_inode_pages() would cause the read() to > return -EIO because invalidate cleared PageUptodate() at the wrong time. > > We no longer clear PageUptodate, so I think this is stale code? Perhaps > you could check with the original author ... Which code do you think might be stale? We need the !PageUptodate check to catch IO errors and we need the !page->mapping check to catch invalidates. Am a bit confused.
