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>
---
mm/filemap.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 1a6beaf69f49..029787fda56b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2185,6 +2185,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
pgoff_t index;
pgoff_t last_index;
pgoff_t prev_index;
+ ssize_t this_written = 0;
unsigned long offset; /* offset into pagecache page */
unsigned int prev_offset;
int error = 0;
@@ -2207,6 +2208,14 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
cond_resched();
find_page:
+ /*
+ * 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 (this_written && (iocb->ki_flags & IOCB_WAITQ))
+ iocb->ki_flags |= IOCB_NOWAIT;
+
if (fatal_signal_pending(current)) {
error = -EINTR;
goto out;
@@ -2239,7 +2248,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
* serialisations and why it's safe.
*/
if (iocb->ki_flags & IOCB_WAITQ) {
- if (written) {
+ if (this_written) {
put_page(page);
goto out;
}
@@ -2328,7 +2337,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
prev_offset = offset;
put_page(page);
- written += ret;
+ this_written += ret;
if (!iov_iter_count(iter))
goto out;
if (ret < nr) {
@@ -2448,6 +2457,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
*ppos = ((loff_t)index << PAGE_SHIFT) + offset;
file_accessed(filp);
+ written += this_written;
return written ? written : error;
}
EXPORT_SYMBOL_GPL(generic_file_buffered_read);
--
2.28.0
--
Jens Axboe
