From 0557a0d9a14e449c31f1e2c626cf3b41b7cfa2b8 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Sat, 17 Oct 2020 08:31:29 -0600 Subject: [PATCH 2411/2944] mm: mark async iocb read as NOWAIT once some data has been copied task #31332859 commit 13bd691421bc191a402d2e0d3da5f248d170a632 upstream. Once we've copied some data for an iocb that is marked with IOCB_WAITQ, we should no longer attempt to async lock a new page. Instead make sure we return the copied amount, and let the caller retry, instead of returning -EIOCBQUEUED for a new page. This should only be possible with read-ahead disabled on the below device, and multiple threads racing on the same file. Haven't been able to reproduce on anything else. Cc: stable@vger.kernel.org # v5.9 Fixes: 1a0a7853b901 ("mm: support async buffered reads in generic_file_buffered_read()") Reported-by: Kent Overstreet Signed-off-by: Jens Axboe Signed-off-by: Hao Xu Reviewed-by: Joseph Qi --- mm/filemap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 9c33806..8663142 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2142,6 +2142,14 @@ static ssize_t generic_file_buffered_read(struct kiocb *iocb, last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; offset = *ppos & ~PAGE_MASK; + /* + * If we've already successfully copied some data, then we + * can no longer safely return -EIOCBQUEUED. Hence mark + * an async read NOWAIT at that point. + */ + if (written && (iocb->ki_flags & IOCB_WAITQ)) + iocb->ki_flags |= IOCB_NOWAIT; + for (;;) { struct page *page; pgoff_t end_index; -- 1.8.3.1