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@xxxxxxxxxxxxxxx # v5.9
Fixes: 1a0a7853b901 ("mm: support async buffered reads in generic_file_buffered_read()")
Reported-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
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
