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Sat, 17 Oct 2020 13:07:27 -0700 (PDT) From: Jens Axboe Subject: [PATCH v3] mm: mark async iocb read as NOWAIT once some data has been, copied To: linux-mm , Andrew Morton , Johannes Weiner , Kent Overstreet , Matthew Wilcox Message-ID: Date: Sat, 17 Oct 2020 14:07:26 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 --- V3 - Place the 'written' check up top so we catch cases where 'written' is already passed in as non-zero (Kent) mm/filemap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 1a6beaf69f49..e4101b5bfa82 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2199,6 +2199,14 @@ 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; -- 2.28.0 -- Jens Axboe