From: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Subject: writeback: fix negative bdi max pause
Toralf runs trinity on UML/i386. After some time it hangs and the last
message line is
BUG: soft lockup - CPU#0 stuck for 22s! [trinity-child0:1521]
It's found that pages_dirtied becomes very large. More than 1000000000
pages in this case:
period = HZ * pages_dirtied / task_ratelimit;
BUG_ON(pages_dirtied > 2000000000);
BUG_ON(pages_dirtied > 1000000000); <---------
UML debug printf shows that we got negative pause here:
ick: pause : -984
ick: pages_dirtied : 0
ick: task_ratelimit: 0
pause:
+ if (pause < 0) {
+ extern int printf(char *, ...);
+ printf("ick : pause : %li\n", pause);
+ printf("ick: pages_dirtied : %lu\n", pages_dirtied);
+ printf("ick: task_ratelimit: %lu\n", task_ratelimit);
+ BUG_ON(1);
+ }
trace_balance_dirty_pages(bdi,
Since pause is bounded by [min_pause, max_pause] where min_pause is also
bounded by max_pause. It's suspected and demonstrated that the max_pause
calculation goes wrong:
ick: pause : -717
ick: min_pause : -177
ick: max_pause : -717
ick: pages_dirtied : 14
ick: task_ratelimit: 0
The problem lies in the two "long = unsigned long" assignments in
bdi_max_pause() which might go negative if the highest bit is 1, and the
min_t(long, ...) check failed to protect it falling under 0. Fix all of
them by using "unsigned long" throughout the function.
Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Reported-by: Toralf Förster <toralf.foerster@xxxxxx>
Tested-by: Toralf Förster <toralf.foerster@xxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Richard Weinberger <richard@xxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff -puN mm/page-writeback.c~writeback-fix-negative-bdi-max-pause mm/page-writeback.c
--- a/mm/page-writeback.c~writeback-fix-negative-bdi-max-pause
+++ a/mm/page-writeback.c
@@ -1210,11 +1210,11 @@ static unsigned long dirty_poll_interval
return 1;
}
-static long bdi_max_pause(struct backing_dev_info *bdi,
- unsigned long bdi_dirty)
+static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
+ unsigned long bdi_dirty)
{
- long bw = bdi->avg_write_bandwidth;
- long t;
+ unsigned long bw = bdi->avg_write_bandwidth;
+ unsigned long t;
/*
* Limit pause time for small memory systems. If sleeping for too long
@@ -1226,7 +1226,7 @@ static long bdi_max_pause(struct backing
t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
t++;
- return min_t(long, t, MAX_PAUSE);
+ return min_t(unsigned long, t, MAX_PAUSE);
}
static long bdi_min_pause(struct backing_dev_info *bdi,
_
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