Vivek Goyal wrote: > Hi Gui, > > Thanks for the report. I use cgroup_path() for debugging. I guess that > cgroup_path() was passed null cgrp pointer that's why it crashed. > > If yes, then it is strange though. I call cgroup_path() only after > grabbing a refenrece to css object. (I am assuming that if I have a valid > reference to css object then css->cgrp can't be null). I think so too... > > Anyway, can you please try out following patch and see if it fixes your > crash. > > --- > block/elevator-fq.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > Index: linux11/block/elevator-fq.c > =================================================================== > --- linux11.orig/block/elevator-fq.c 2009-05-05 15:38:06.000000000 -0400 > +++ linux11/block/elevator-fq.c 2009-05-06 11:55:47.000000000 -0400 > @@ -125,6 +125,9 @@ static void io_group_path(struct io_grou > unsigned short id = iog->iocg_id; > struct cgroup_subsys_state *css; > > + /* For error case */ > + buf[0] = '\0'; > + > rcu_read_lock(); > > if (!id) > @@ -137,15 +140,12 @@ static void io_group_path(struct io_grou > if (!css_tryget(css)) > goto out; > > - cgroup_path(css->cgroup, buf, buflen); > + if (css->cgroup) According to CR2, when kernel crashing, css->cgroup equals 0x00000100. So i guess this patch won't fix this issue. > + cgroup_path(css->cgroup, buf, buflen); > > css_put(css); > - > - rcu_read_unlock(); > - return; > out: > rcu_read_unlock(); > - buf[0] = '\0'; > return; > } > #endif > > BTW, I tried following equivalent script and I can't see the crash on > my system. Are you able to hit it regularly? yes, it's 50% chance that i can reproduce it. i'v attached the rwio source code. > > Instead of killing the tasks I also tried moving the tasks into root cgroup > and then deleting test1 and test2 groups, that also did not produce any crash. > (Hit a different bug though after 5-6 attempts :-) > > As I mentioned in the patchset, currently we do have issues with group > refcounting and cgroup/group going away. Hopefully in next version they > all should be fixed up. But still, it is nice to hear back... > > -- Regards Gui Jianfeng
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