----- "Dave Anderson" <anderson@xxxxxxxxxx> wrote: > ----- "Michael Holzheu" <holzheu@xxxxxxxxxxxxxxxxxx> 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@xxxxxx) > > where this was his patch posting -- which fixed refresh_hlist_task_table_v2(): > > 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 Hi Michael, Works well -- it's a rare occurrance, but the patch uncovered a total of seven missing tasks in a test run on a sample set of 50 "v3" dumpfiles. Queued for next release. 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@xxxxxxxxxx > > https://www.redhat.com/mailman/listinfo/crash-utility > > -- > Crash-utility mailing list > Crash-utility@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/crash-utility -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
