From 8751853091998cd31e9e5f1e8206280155af8921 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 4 Jul 2019 15:14:49 -0700
Subject: [PATCH] swap_readpage(): avoid blk_wake_io_task() if !synchronous
swap_readpage() sets waiter = bio->bi_private even if synchronous = F,
this means that the caller can get the spurious wakeup after return.
This can be fatal if blk_wake_io_task() does
set_current_state(TASK_RUNNING) after the caller does
set_special_state(), in the worst case the kernel can crash in
do_task_dead().
Link: http://lkml.kernel.org/r/20190704160301.GA5956@redhat.com
Fixes: 0619317ff8baa2d ("block: add polled wakeup task helper")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Qian Cai <cai@lca.pw>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/page_io.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c
index 189415852077e..a39aac2f8c8d6 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -137,8 +137,10 @@ static void end_swap_bio_read(struct bio *bio)
unlock_page(page);
WRITE_ONCE(bio->bi_private, NULL);
bio_put(bio);
- blk_wake_io_task(waiter);
- put_task_struct(waiter);
+ if (waiter) {
+ blk_wake_io_task(waiter);
+ put_task_struct(waiter);
+ }
}
int generic_swapfile_activate(struct swap_info_struct *sis,
@@ -395,11 +397,12 @@ int swap_readpage(struct page *page, bool synchronous)
* Keep this task valid during swap readpage because the oom killer may
* attempt to access it in the page fault retry time check.
*/
- get_task_struct(current);
- bio->bi_private = current;
bio_set_op_attrs(bio, REQ_OP_READ, 0);
- if (synchronous)
+ if (synchronous) {
bio->bi_opf |= REQ_HIPRI;
+ get_task_struct(current);
+ bio->bi_private = current;
+ }
count_vm_event(PSWPIN);
bio_get(bio);
qc = submit_bio(bio);
--
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