Commits
Fengguang Wu committed e3b6c655b91
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>