| From e3b6c655b91e01a1dade056cfa358581b47a5351 Mon Sep 17 00:00:00 2001 |
| From: Fengguang Wu <fengguang.wu@intel.com> |
| Date: Wed, 16 Oct 2013 13:47:03 -0700 |
| Subject: writeback: fix negative bdi max pause |
| |
| From: Fengguang Wu <fengguang.wu@intel.com> |
| |
| commit e3b6c655b91e01a1dade056cfa358581b47a5351 upstream. |
| |
| 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@intel.com> |
| Reported-by: Toralf Förster <toralf.foerster@gmx.de> |
| Tested-by: Toralf Förster <toralf.foerster@gmx.de> |
| Reviewed-by: Jan Kara <jack@suse.cz> |
| Cc: Richard Weinberger <richard@nod.at> |
| Cc: Geert Uytterhoeven <geert@linux-m68k.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| mm/page-writeback.c | 10 +++++----- |
| 1 file changed, 5 insertions(+), 5 deletions(-) |
| |
| --- a/mm/page-writeback.c |
| +++ b/mm/page-writeback.c |
| @@ -1104,11 +1104,11 @@ 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 |
| @@ -1120,7 +1120,7 @@ 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, |
