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| author | Fengguang Wu <fengguang.wu@intel.com> | 2013-10-16 13:47:03 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-10-16 21:35:53 -0700 |
| commit | e3b6c655b91e01a1dade056cfa358581b47a5351 (patch) | |
| tree | f2d77b6746591fa853bbb249ff65c7f2316929c1 /mm/page-writeback.c | |
| parent | 5e9dd373dea43f61f5d3ce8b6667377a02c6fd42 (diff) | |
| download | lwn-e3b6c655b91e01a1dade056cfa358581b47a5351.tar.gz lwn-e3b6c655b91e01a1dade056cfa358581b47a5351.zip | |
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@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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index f5236f804aa6..63807583d8e8 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1210,11 +1210,11 @@ static unsigned long dirty_poll_interval(unsigned long dirty, 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_dev_info *bdi, 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, |