linux-toradex.git/kernel/debug/kdb/kdb_bt.c, branch v6.8-rc5

kdb: Adopt scheduler's task classification

2021-11-03T17:21:37+00:00

Currently kdb contains some open-coded routines to generate a summary
character for each task. This code currently issues warnings, is
almost certainly broken and won't make sense to any kernel dev who
has ever used /proc to examine task states.

Fix both the warning and the potential for confusion by adopting the
scheduler's task classification. Whilst doing this we also simplify the
filtering by using mask strings directly (which means we don't have to
guess all the characters the scheduler might give us).

Unfortunately we can't quite match the scheduler classification completely.
We add four extra states: - for idle loops and i, m and s for sleeping
system daemons (which means kthreads in one of the I, M and S states).
These extra states are used to manage the filters for tools to make the
output of ps and bta less noisy.

Note: The Fixes below is the last point the original dubious code was
      moved; it was not introduced by that patch. However it gives us
      the last point to which this patch can be easily backported.
      Happily that should be enough to cover the introduction of
      CONFIG_WERROR!

Fixes: 2f064a59a11f ("sched: Change task_struct::state")
Link: https://lore.kernel.org/r/20211102173158.3315227-1-daniel.thompson@linaro.org
Reviewed-by: Douglas Anderson 
Signed-off-by: Daniel Thompson

kdb: Use newer api for tasklist scanning

2020-09-08T13:36:46+00:00

This kills using the do_each_thread/while_each_thread combo to
iterate all threads and uses for_each_process_thread() instead,
maintaining semantics. while_each_thread() is ultimately racy
and deprecated;  although in this particular case there is no
concurrency so it doesn't matter. Still lets trivially get rid
of two more users.

Acked-by: Oleg Nesterov 
Signed-off-by: Davidlohr Bueso 
Link: https://lore.kernel.org/r/20200907203206.21293-1-dave@stgolabs.net
Signed-off-by: Daniel Thompson

kernel: rename show_stack_loglvl() => show_stack()

2020-06-09T16:39:13+00:00

Now the last users of show_stack() got converted to use an explicit log
level, show_stack_loglvl() can drop it's redundant suffix and become once
again well known show_stack().

Signed-off-by: Dmitry Safonov 
Signed-off-by: Andrew Morton 
Link: http://lkml.kernel.org/r/20200418201944.482088-51-dima@arista.com
Signed-off-by: Linus Torvalds

kdb: don't play with console_loglevel

2020-06-09T16:39:12+00:00

Print the stack trace with KERN_EMERG - it should be always visible.

Playing with console_loglevel is a bad idea as there may be more messages
printed than wanted.  Also the stack trace might be not printed at all if
printk() was deferred and console_loglevel was raised back before the
trace got flushed.

Unfortunately, after rebasing on commit 2277b492582d ("kdb: Fix stack
crawling on 'running' CPUs that aren't the master"), kdb_show_stack() uses
now kdb_dump_stack_on_cpu(), which for now won't be converted as it uses
dump_stack() instead of show_stack().

Convert for now the branch that uses show_stack() and remove
console_loglevel exercise from that case.

Signed-off-by: Dmitry Safonov 
Signed-off-by: Andrew Morton 
Reviewed-by: Douglas Anderson 
Acked-by: Daniel Thompson 
Cc: Jason Wessel 
Link: http://lkml.kernel.org/r/20200418201944.482088-48-dima@arista.com
Signed-off-by: Linus Torvalds

kdb: Gid rid of implicit setting of the current task / regs

2020-01-31T17:34:00+00:00

Some (but not all?) of the kdb backtrace paths would cause the
kdb_current_task and kdb_current_regs to remain changed.  As discussed
in a review of a previous patch [1], this doesn't seem intuitive, so
let's fix that.

...but, it turns out that there's actually no longer any reason to set
the current task / current regs while backtracing anymore anyway.  As
of commit 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs
that aren't the master") if we're backtracing on a task running on a
CPU we ask that CPU to do the backtrace itself.  Linux can do that
without anything fancy.  If we're doing backtrace on a sleeping task
we can also do that fine without updating globals.  So this patch
mostly just turns into deleting a bunch of code.

[1] https://lore.kernel.org/r/20191010150735.dhrj3pbjgmjrdpwr@holly.lan

Signed-off-by: Douglas Anderson 
Link: https://lore.kernel.org/r/20191109111624.4.Ibc3d982bbeb9e46872d43973ba808cd4c79537c7@changeid
Signed-off-by: Daniel Thompson

kdb: Remove special case logic from kdb_read()

2019-10-28T12:07:57+00:00

kdb_read() contains special case logic to force it exit after reading
a single character. We can remove all the special case logic by directly
calling the function to read a single character instead. This also
allows us to tidy up the function prototype which, because it now matches
getchar(), we can also rename in order to make its role clearer.

This does involve some extra code to handle btaprompt properly but we
don't mind the new lines of code here because the old code had some
interesting problems (bad newline handling, treating unexpected
characters like ).

Signed-off-by: Daniel Thompson 
Reviewed-by: Douglas Anderson 
Link: https://lore.kernel.org/r/20191025073328.643-4-daniel.thompson@linaro.org

kdb: Fix stack crawling on 'running' CPUs that aren't the master

2019-10-10T15:28:48+00:00

In kdb when you do 'btc' (back trace on CPU) it doesn't necessarily
give you the right info.  Specifically on many architectures
(including arm64, where I tested) you can't dump the stack of a
"running" process that isn't the process running on the current CPU.
This can be seen by this:

 echo SOFTLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT
 # wait 2 seconds
 g

Here's what I see now on rk3399-gru-kevin.  I see the stack crawl for
the CPU that handled the sysrq but everything else just shows me stuck
in __switch_to() which is bogus:

======

[0]kdb> btc
btc: cpu status: Currently on cpu 0
Available cpus: 0, 1-3(I), 4, 5(I)
Stack traceback for pid 0
0xffffff801101a9c0        0        0  1    0   R  0xffffff801101b3b0 *swapper/0
Call trace:
 dump_backtrace+0x0/0x138
 ...
 kgdb_compiled_brk_fn+0x34/0x44
 ...
 sysrq_handle_dbg+0x34/0x5c
Stack traceback for pid 0
0xffffffc0f175a040        0        0  1    1   I  0xffffffc0f175aa30  swapper/1
Call trace:
 __switch_to+0x1e4/0x240
 0xffffffc0f65616c0
Stack traceback for pid 0
0xffffffc0f175d040        0        0  1    2   I  0xffffffc0f175da30  swapper/2
Call trace:
 __switch_to+0x1e4/0x240
 0xffffffc0f65806c0
Stack traceback for pid 0
0xffffffc0f175b040        0        0  1    3   I  0xffffffc0f175ba30  swapper/3
Call trace:
 __switch_to+0x1e4/0x240
 0xffffffc0f659f6c0
Stack traceback for pid 1474
0xffffffc0dde8b040     1474      727  1    4   R  0xffffffc0dde8ba30  bash
Call trace:
 __switch_to+0x1e4/0x240
 __schedule+0x464/0x618
 0xffffffc0dde8b040
Stack traceback for pid 0
0xffffffc0f17b0040        0        0  1    5   I  0xffffffc0f17b0a30  swapper/5
Call trace:
 __switch_to+0x1e4/0x240
 0xffffffc0f65dd6c0

===

The problem is that 'btc' eventually boils down to
  show_stack(task_struct, NULL);

...and show_stack() doesn't work for "running" CPUs because their
registers haven't been stashed.

On x86 things might work better (I haven't tested) because kdb has a
special case for x86 in kdb_show_stack() where it passes the stack
pointer to show_stack().  This wouldn't work on arm64 where the stack
crawling function seems needs the "fp" and "pc", not the "sp" which is
presumably why arm64's show_stack() function totally ignores the "sp"
parameter.

NOTE: we _can_ get a good stack dump for all the cpus if we manually
switch each one to the kdb master and do a back trace.  AKA:
  cpu 4
  bt
...will give the expected trace.  That's because now arm64's
dump_backtrace will now see that "tsk == current" and go through a
different path.

In this patch I fix the problems by catching a request to stack crawl
a task that's running on a CPU and then I ask that CPU to do the stack
crawl.

NOTE: this will (presumably) change what stack crawls are printed for
x86 machines.  Now kdb functions will show up in the stack crawl.
Presumably this is OK but if it's not we can go back and add a special
case for x86 again.

Signed-off-by: Douglas Anderson 
Acked-by: Will Deacon 
Signed-off-by: Daniel Thompson

kdb: Fix "btc " crash if the CPU didn't round up

2019-10-10T15:28:14+00:00

I noticed that when I did "btc " and the CPU I passed in hadn't
rounded up that I'd crash.  I was going to copy the same fix from
commit 162bc7f5afd7 ("kdb: Don't back trace on a cpu that didn't round
up") into the "not all the CPUs" case, but decided it'd be better to
clean things up a little bit.

This consolidates the two code paths.  It is _slightly_ wasteful in in
that the checks for "cpu" being too small or being offline isn't
really needed when we're iterating over all online CPUs, but that
really shouldn't hurt.  Better to have the same code path.

While at it, eliminate at least one slightly ugly (and totally
needless) recursive use of kdb_parse().

Signed-off-by: Douglas Anderson 
Acked-by: Will Deacon 
Signed-off-by: Daniel Thompson

kdb: Remove unused "argcount" param from kdb_bt1(); make btaprompt bool

2019-10-10T15:28:08+00:00

The kdb_bt1() had a mysterious "argcount" parameter passed in (always
the number 5, by the way) and never used.  Presumably this is just old
cruft.  Remove it.  While at it, upgrade the btaprompt parameter to a
full fledged bool instead of an int.

Signed-off-by: Douglas Anderson 
Acked-by: Will Deacon 
Signed-off-by: Daniel Thompson

kdb: Don't back trace on a cpu that didn't round up

2018-12-30T08:31:23+00:00

If you have a CPU that fails to round up and then run 'btc' you'll end
up crashing in kdb becaue we dereferenced NULL.  Let's add a check.
It's wise to also set the task to NULL when leaving the debugger so
that if we fail to round up on a later entry into the debugger we
won't backtrace a stale task.

Signed-off-by: Douglas Anderson 
Acked-by: Daniel Thompson 
Signed-off-by: Daniel Thompson