mm: never attempt async page lock if we've transferred data already

We catch the case where we enter generic_file_buffered_read() with data
already transferred, but we also need to be careful not to allow an async
page lock if we're looping transferring data. If not, we could be
returning -EIOCBQUEUED instead of the transferred amount, and it could
result in double waitqueue additions as well.

Cc: stable@vger.kernel.org # v5.9
Fixes: 1a0a7853b901 ("mm: support async buffered reads in generic_file_buffered_read()")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/mm/filemap.c b/mm/filemap.c
index d5e7c20..3ebbe64 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2347,10 +2347,15 @@ page_ok:
 
 page_not_up_to_date:
                /* Get exclusive access to the page ... */
-               if (iocb->ki_flags & IOCB_WAITQ)
+               if (iocb->ki_flags & IOCB_WAITQ) {
+                       if (written) {
+                               put_page(page);
+                               goto out;
+                       }
                        error = lock_page_async(page, iocb->ki_waitq);
-               else
+               } else {
                        error = lock_page_killable(page);
+               }
                if (unlikely(error))
                        goto readpage_error;
 
@@ -2393,10 +2398,15 @@ readpage:
                }
 
                if (!PageUptodate(page)) {
-                       if (iocb->ki_flags & IOCB_WAITQ)
+                       if (iocb->ki_flags & IOCB_WAITQ) {
+                               if (written) {
+                                       put_page(page);
+                                       goto out;
+                               }
                                error = lock_page_async(page, iocb->ki_waitq);
-                       else
+                       } else {
                                error = lock_page_killable(page);
+                       }
 
                        if (unlikely(error))
                                goto readpage_error;