From: Kent Overstreet kent.overstreet@gmail.com

commit 3644e2d2dda78e21edd8f5415b6d7ab03f5f54f3 upstream.

If iter->count is 0 and iocb->ki_pos is page aligned, this causes nr_pages to be 0.

Then in generic_file_buffered_read_get_pages() find_get_pages_contig() returns 0 - because we asked for 0 pages, so we call generic_file_buffered_read_no_cached_page() which attempts to add a page to the page cache, which fails with -EEXIST, and then we loop. Oops...

Signed-off-by: Kent Overstreet kent.overstreet@gmail.com Reported-by: Jens Axboe axboe@kernel.dk Reviewed-by: Jens Axboe axboe@kernel.dk Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Suraj Jitindar Singh surajjs@amazon.com --- mm/filemap.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c index 3a983bc1a71c..3b0d8c6dd587 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2203,6 +2203,9 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,

if (unlikely(*ppos >= inode->i_sb->s_maxbytes)) return 0; + if (unlikely(!iov_iter_count(iter))) + return 0; + iov_iter_truncate(iter, inode->i_sb->s_maxbytes);

index = *ppos >> PAGE_SHIFT;