Re: [Crash-utility] [PATCH] Show missing tasks in ps

----- "Michael Holzheu" <holzheu(a)linux.vnet.ibm.com&gt; wrote: > Hi Dave, > > I got an s390x dump of a Linux 2.6.36 system, where a task (kmcheck, pid=44) is > missing in the ps output. I debugged the problem and I think that I found the > reason: > > It looks like that crash does not walk the linked list of the pid hash table > to the end, if it finds a NULL pointer in the pid.tasks[PIDTYPE_PID=0] > array. Unfortunately, for the struct pid that is before our lost task in the > linked list this condition is true. Therefore crash does not find our task. That sounds similar to the fix Bob Montgomery made in 5.0.7: - Fix for the potential to miss one or more tasks in 2.6.23 and earlier kernels, presumably due to catching an entry the kernel's pid_hash[] chain in transition. Without the patch, the task will simply not be seen in the gathered task list. (bob.montgomery(a)hp.com) where this was his patch posting -- which fixed refresh_hlist_task_table_v2(): [Crash-utility] Missing PID 1 is crash problem with losing tasks https://www.redhat.com/archives/crash-utility/2010-August/msg00049.html and where your patch fixes refresh_hlist_task_table_v3(). I'll give it a test run... Thanks, Dave

> The attached patch seems to fix this problem. > > Here my crash debug log with the 2.6.36 dump: > --------------------------------------------- > Task "kmcheck" is in hash slot 2941 in the linked list at position 2: > > crash> print pid_hash[2941] > $4 = { > first = 0x3f5fb7f8 > } > > crash> upid > struct upid { > int nr; > struct pid_namespace *ns; > struct hlist_node pid_chain; > } > SIZE: 32 > > crash> upid.pid_chain > struct upid { > [16] struct hlist_node pid_chain; > } > > crash> eval 0x3f5fb7f8 - 16 > hexadecimal: 3f5fb7e8 > > crash> upid 3f5fb7e8 <<<<---- the first upid in the list > struct upid { > nr = 565, > ns = 0x81d8f8, > pid_chain = { > next = 0x3edea2b0, > pprev = 0x96554e8 > } > } > > crash> pid > struct pid { > atomic_t count; > unsigned int level; > struct hlist_head tasks[3]; > struct rcu_head rcu; > struct upid numbers[1]; > } > SIZE: 80 > > crash> pid.numbers > struct pid { > [48] struct upid numbers[1]; > } > > crash> eval 3f5fb7e8 - 48 > hexadecimal: 3f5fb7b8 > > crash> pid 3f5fb7b8 > struct pid { > count = { > counter = 1 > }, > level = 0, > tasks = {{ > first = 0x0 <<<----------- tasks[0] is NULL > }, { > first = 0x3d488620 > }, { > first = 0x0 > }}, > rcu = { > next = 0x5a5a5a5a5a5a5a5a, > func = 0x5a5a5a5a5a5a5a5a > }, > numbers = {{ > nr = 565, > ns = 0x81d8f8, > pid_chain = { > next = 0x3edea2b0, <<<--------- Pointer to second element in > list > pprev = 0x96554e8 > } > }} > } > > crash> eval 0x3edea2b0 - 16 > hexadecimal: 3edea2a0 <<<-- The second upid in the list > > crash> upid 0x3edea2a0 > struct upid { > nr = 44, <<<--- Our missing pid=44 (kmcheck) > ns = 0x81d8f8, > pid_chain = { > next = 0x0, > pprev = 0x3f5fb7f8 > } > } > > crash> eval 0x3edea2a0 - 48 > hexadecimal: 3edea270 > > crash> pid 3edea270 > struct pid { > count = { > counter = 5 > }, > level = 0, > tasks = {{ > first = 0x3e799908 <<<--- Pointer to our task_struct.pids > }, { > first = 0x0 > }, { > first = 0x0 > }}, > rcu = { > next = 0x5a5a5a5a5a5a5a5a, > func = 0x5a5a5a5a5a5a5a5a > }, > numbers = {{ > nr = 44, > ns = 0x81d8f8, > pid_chain = { > next = 0x0, > pprev = 0x3f5fb7f8 > } > }} > } > > crash> task_struct.pids > struct task_struct { > [712] struct pid_link pids[3]; > } > > crash> eval 0x3e799908 - 712 > hexadecimal: 3e799640 > > crash> task_struct 3e799640 | grep comm > comm = "kmcheck\000\000\000\000\000\000\000\000", <<<--- here it is > --- > task.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- a/task.c > +++ b/task.c > @@ -2006,7 +2006,7 @@ do_chained: > } > > if (pid_tasks_0 == 0) > - continue; > + goto chain_next; > > next = pid_tasks_0 - OFFSET(task_struct_pids); > > @@ -2042,7 +2042,7 @@ do_chained: > } > > cnt++; > - > +chain_next: > if (pnext) { > kpp = pnext; > upid = pnext - OFFSET(upid_pid_chain); > > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility