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mm: mark async iocb read as NOWAIT once some data has been copied 

upstream commit id: 13bd691421bc191a402d2e0d3da5f248d170a632

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 <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ni Xun <richardni@tencent.com>
This commit is contained in:
Jens Axboe 2020-10-17 08:31:29 -06:00 committed by arafatms
parent 0953150e68
commit 5e72efeb0b
1 changed files with 8 additions and 0 deletions
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8
mm/filemap.c
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@ -2078,6 +2078,14 @@ 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;