From: Jan Kara jack@suse.cz
commit 5c72feee3e45b40a3c96c7145ec422899d0e8964 upstream.
When handling a page fault, we drop mmap_sem to start async readahead so that we don't block on IO submission with mmap_sem held. However there's no point to drop mmap_sem in case readahead is disabled. Handle that case to avoid pointless dropping of mmap_sem and retrying the fault. This was actually reported to block mlockall(MCL_CURRENT) indefinitely.
Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations") Reported-by: Minchan Kim minchan@kernel.org Reported-by: Robert Stupp snazy@gmx.de Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Josef Bacik josef@toxicpanda.com Reviewed-by: Minchan Kim minchan@kernel.org Link: http://lkml.kernel.org/r/20200212101356.30759-1-jack@suse.cz Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Cc: SeongJae Park sjpark@amazon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/filemap.c +++ b/mm/filemap.c @@ -2438,7 +2438,7 @@ static struct file *do_async_mmap_readah pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */ - if (vmf->vma->vm_flags & VM_RAND_READ) + if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages) return fpin; if (ra->mmap_miss > 0) ra->mmap_miss--;