mm/memory.c: release locked page in do_swap_page()

James reported a bug in swap paging-in from his testing.  It is that
do_swap_page doesn't release locked page so system hang-up happens due
to a deadlock on PG_locked.

It was introduced by 0bcac06f27d7 ("mm, swap: skip swapcache for swapin
of synchronous device") because I missed swap cache hit places to update
swapcache variable to work well with other logics against swapcache in
do_swap_page.

This patch fixes it.

Debugged by James Bottomley.

Link: http://lkml.kernel.org/r/<1514407817.4169.4.camel@HansenPartnership.com>
Link: http://lkml.kernel.org/r/20180102235606.GA19438@bbox
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: James Bottomley <James.Bottomley@hansenpartnership.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index ca5674c..7930046 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2857,8 +2857,11 @@ int do_swap_page(struct vm_fault *vmf)
        int ret = 0;
        bool vma_readahead = swap_use_vma_readahead();
 
-       if (vma_readahead)
+       if (vma_readahead) {
                page = swap_readahead_detect(vmf, &swap_ra);
+               swapcache = page;
+       }
+
        if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) {
                if (page)
                        put_page(page);
@@ -2889,9 +2892,12 @@ int do_swap_page(struct vm_fault *vmf)
 
 
        delayacct_set_flag(DELAYACCT_PF_SWAPIN);
-       if (!page)
+       if (!page) {
                page = lookup_swap_cache(entry, vma_readahead ? vma : NULL,
                                         vmf->address);
+               swapcache = page;
+       }
+
        if (!page) {
                struct swap_info_struct *si = swp_swap_info(entry);