linux-toradex.git/kernel/trace, branch v5.14-rc4

ftrace: Remove redundant initialization of variable ret

2021-07-23T12:46:02+00:00

The variable ret is being initialized with a value that is never
read, it is being updated later on. The assignment is redundant and
can be removed.

Link: https://lkml.kernel.org/r/20210721120915.122278-1-colin.king@canonical.com

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King 
Signed-off-by: Steven Rostedt (VMware)

ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary

2021-07-23T12:45:53+00:00

synchronize_rcu_tasks_rude() triggers IPIs and forces rescheduling on
all CPUs. It is a costly operation and, when targeting nohz_full CPUs,
very disrupting (hence the name). So avoid calling it when 'old_hash'
doesn't need to be freed.

Link: https://lkml.kernel.org/r/20210721114726.1545103-1-nsaenzju@redhat.com

Signed-off-by: Nicolas Saenz Julienne 
Signed-off-by: Steven Rostedt (VMware)

tracing: Clean up alloc_synth_event()

2021-07-23T12:45:30+00:00

alloc_synth_event() currently has the following code to initialize the
event fields and dynamic_fields:

	for (i = 0, j = 0; i < n_fields; i++) {
		event->fields[i] = fields[i];

		if (fields[i]->is_dynamic) {
			event->dynamic_fields[j] = fields[i];
			event->dynamic_fields[j]->field_pos = i;
			event->dynamic_fields[j++] = fields[i];
			event->n_dynamic_fields++;
		}
	}

1) It would make more sense to have all fields keep track of their
   field_pos.

2) event->dynmaic_fields[j] is assigned twice for no reason.

3) We can move updating event->n_dynamic_fields outside the loop, and just
   assign it to j.

This combination makes the code much cleaner.

Link: https://lkml.kernel.org/r/20210721195341.29bb0f77@oasis.local.home

Signed-off-by: Steven Rostedt (VMware)

tracing/histogram: Rename "cpu" to "common_cpu"

2021-07-23T12:44:47+00:00

Currently the histogram logic allows the user to write "cpu" in as an
event field, and it will record the CPU that the event happened on.

The problem with this is that there's a lot of events that have "cpu"
as a real field, and using "cpu" as the CPU it ran on, makes it
impossible to run histograms on the "cpu" field of events.

For example, if I want to have a histogram on the count of the
workqueue_queue_work event on its cpu field, running:

 ># echo 'hist:keys=cpu' > events/workqueue/workqueue_queue_work/trigger

Gives a misleading and wrong result.

Change the command to "common_cpu" as no event should have "common_*"
fields as that's a reserved name for fields used by all events. And
this makes sense here as common_cpu would be a field used by all events.

Now we can even do:

 ># echo 'hist:keys=common_cpu,cpu if cpu < 100' > events/workqueue/workqueue_queue_work/trigger
 ># cat events/workqueue/workqueue_queue_work/hist
 # event histogram
 #
 # trigger info: hist:keys=common_cpu,cpu:vals=hitcount:sort=hitcount:size=2048 if cpu < 100 [active]
 #

 { common_cpu:          0, cpu:          2 } hitcount:          1
 { common_cpu:          0, cpu:          4 } hitcount:          1
 { common_cpu:          7, cpu:          7 } hitcount:          1
 { common_cpu:          0, cpu:          7 } hitcount:          1
 { common_cpu:          0, cpu:          1 } hitcount:          1
 { common_cpu:          0, cpu:          6 } hitcount:          2
 { common_cpu:          0, cpu:          5 } hitcount:          2
 { common_cpu:          1, cpu:          1 } hitcount:          4
 { common_cpu:          6, cpu:          6 } hitcount:          4
 { common_cpu:          5, cpu:          5 } hitcount:         14
 { common_cpu:          4, cpu:          4 } hitcount:         26
 { common_cpu:          0, cpu:          0 } hitcount:         39
 { common_cpu:          2, cpu:          2 } hitcount:        184

Now for backward compatibility, I added a trick. If "cpu" is used, and
the field is not found, it will fall back to "common_cpu" and work as
it did before. This way, it will still work for old programs that use
"cpu" to get the actual CPU, but if the event has a "cpu" as a field, it
will get that event's "cpu" field, which is probably what it wants
anyway.

I updated the tracefs/README to include documentation about both the
common_timestamp and the common_cpu. This way, if that text is present in
the README, then an application can know that common_cpu is supported over
just plain "cpu".

Link: https://lkml.kernel.org/r/20210721110053.26b4f641@oasis.local.home

Cc: Namhyung Kim 
Cc: Ingo Molnar 
Cc: Andrew Morton 
Cc: stable@vger.kernel.org
Fixes: 8b7622bf94a44 ("tracing: Add cpu field for hist triggers")
Reviewed-by: Tom Zanussi 
Reviewed-by: Masami Hiramatsu 
Signed-off-by: Steven Rostedt (VMware)

tracing: Synthetic event field_pos is an index not a boolean

2021-07-23T12:43:04+00:00

Performing the following:

 ># echo 'wakeup_lat s32 pid; u64 delta; char wake_comm[]' > synthetic_events
 ># echo 'hist:keys=pid:__arg__1=common_timestamp.usecs' > events/sched/sched_waking/trigger
 ># echo 'hist:keys=next_pid:pid=next_pid,delta=common_timestamp.usecs-$__arg__1:onmatch(sched.sched_waking).trace(wakeup_lat,$pid,$delta,prev_comm)'\
      > events/sched/sched_switch/trigger
 ># echo 1 > events/synthetic/enable

Crashed the kernel:

 BUG: kernel NULL pointer dereference, address: 000000000000001b
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] PREEMPT SMP
 CPU: 7 PID: 0 Comm: swapper/7 Not tainted 5.13.0-rc5-test+ #104
 Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
 RIP: 0010:strlen+0x0/0x20
 Code: f6 82 80 2b 0b bc 20 74 11 0f b6 50 01 48 83 c0 01 f6 82 80 2b 0b bc
  20 75 ef c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 <80> 3f 00 74 10
  48 89 f8 48 83 c0 01 80 38 9 f8 c3 31
 RSP: 0018:ffffaa75000d79d0 EFLAGS: 00010046
 RAX: 0000000000000002 RBX: ffff9cdb55575270 RCX: 0000000000000000
 RDX: ffff9cdb58c7a320 RSI: ffffaa75000d7b40 RDI: 000000000000001b
 RBP: ffffaa75000d7b40 R08: ffff9cdb40a4f010 R09: ffffaa75000d7ab8
 R10: ffff9cdb4398c700 R11: 0000000000000008 R12: ffff9cdb58c7a320
 R13: ffff9cdb55575270 R14: ffff9cdb58c7a000 R15: 0000000000000018
 FS:  0000000000000000(0000) GS:ffff9cdb5aa00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000000000000001b CR3: 00000000c0612006 CR4: 00000000001706e0
 Call Trace:
  trace_event_raw_event_synth+0x90/0x1d0
  action_trace+0x5b/0x70
  event_hist_trigger+0x4bd/0x4e0
  ? cpumask_next_and+0x20/0x30
  ? update_sd_lb_stats.constprop.0+0xf6/0x840
  ? __lock_acquire.constprop.0+0x125/0x550
  ? find_held_lock+0x32/0x90
  ? sched_clock_cpu+0xe/0xd0
  ? lock_release+0x155/0x440
  ? update_load_avg+0x8c/0x6f0
  ? enqueue_entity+0x18a/0x920
  ? __rb_reserve_next+0xe5/0x460
  ? ring_buffer_lock_reserve+0x12a/0x3f0
  event_triggers_call+0x52/0xe0
  trace_event_buffer_commit+0x1ae/0x240
  trace_event_raw_event_sched_switch+0x114/0x170
  __traceiter_sched_switch+0x39/0x50
  __schedule+0x431/0xb00
  schedule_idle+0x28/0x40
  do_idle+0x198/0x2e0
  cpu_startup_entry+0x19/0x20
  secondary_startup_64_no_verify+0xc2/0xcb

The reason is that the dynamic events array keeps track of the field
position of the fields array, via the field_pos variable in the
synth_field structure. Unfortunately, that field is a boolean for some
reason, which means any field_pos greater than 1 will be a bug (in this
case it was 2).

Link: https://lkml.kernel.org/r/20210721191008.638bce34@oasis.local.home

Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Ingo Molnar 
Cc: Andrew Morton 
Cc: stable@vger.kernel.org
Fixes: bd82631d7ccdc ("tracing: Add support for dynamic strings to synthetic events")
Reviewed-by: Tom Zanussi 
Signed-off-by: Steven Rostedt (VMware)

tracing: Fix bug in rb_per_cpu_empty() that might cause deadloop.

2021-07-22T15:52:33+00:00

The "rb_per_cpu_empty()" misinterpret the condition (as not-empty) when
"head_page" and "commit_page" of "struct ring_buffer_per_cpu" points to
the same buffer page, whose "buffer_data_page" is empty and "read" field
is non-zero.

An error scenario could be constructed as followed (kernel perspective):

1. All pages in the buffer has been accessed by reader(s) so that all of
them will have non-zero "read" field.

2. Read and clear all buffer pages so that "rb_num_of_entries()" will
return 0 rendering there's no more data to read. It is also required
that the "read_page", "commit_page" and "tail_page" points to the same
page, while "head_page" is the next page of them.

3. Invoke "ring_buffer_lock_reserve()" with large enough "length"
so that it shot pass the end of current tail buffer page. Now the
"head_page", "commit_page" and "tail_page" points to the same page.

4. Discard current event with "ring_buffer_discard_commit()", so that
"head_page", "commit_page" and "tail_page" points to a page whose buffer
data page is now empty.

When the error scenario has been constructed, "tracing_read_pipe" will
be trapped inside a deadloop: "trace_empty()" returns 0 since
"rb_per_cpu_empty()" returns 0 when it hits the CPU containing such
constructed ring buffer. Then "trace_find_next_entry_inc()" always
return NULL since "rb_num_of_entries()" reports there's no more entry
to read. Finally "trace_seq_to_user()" returns "-EBUSY" spanking
"tracing_read_pipe" back to the start of the "waitagain" loop.

I've also written a proof-of-concept script to construct the scenario
and trigger the bug automatically, you can use it to trace and validate
my reasoning above:

  https://github.com/aegistudio/RingBufferDetonator.git

Tests has been carried out on linux kernel 5.14-rc2
(2734d6c1b1a089fb593ef6a23d4b70903526fe0c), my fixed version
of kernel (for testing whether my update fixes the bug) and
some older kernels (for range of affected kernels). Test result is
also attached to the proof-of-concept repository.

Link: https://lore.kernel.org/linux-trace-devel/YPaNxsIlb2yjSi5Y@aegistudio/
Link: https://lore.kernel.org/linux-trace-devel/YPgrN85WL9VyrZ55@aegistudio

Cc: stable@vger.kernel.org
Fixes: bf41a158cacba ("ring-buffer: make reentrant")
Suggested-by: Linus Torvalds 
Signed-off-by: Haoran Luo 
Signed-off-by: Steven Rostedt (VMware)

Merge tag 'trace-v5.14-5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

2021-07-17T19:36:51+00:00

Pull tracing fix from Steven Rostedt:
 "Fix the histogram logic from possibly crashing the kernel

  Working on the histogram code, I found that if you dereference a char
  pointer in a trace event that happens to point to user space, it can
  crash the kernel, as it does no checks of that pointer. I have code
  coming that will do this better, so just remove this ability to treat
  character pointers in trace events as stings in the histogram"

* tag 'trace-v5.14-5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Do not reference char * as a string in histograms

tracing: Do not reference char * as a string in histograms

2021-07-15T21:06:13+00:00

The histogram logic was allowing events with char * pointers to be used as
normal strings. But it was easy to crash the kernel with:

 # echo 'hist:keys=filename' > events/syscalls/sys_enter_openat/trigger

And open some files, and boom!

 BUG: unable to handle page fault for address: 00007f2ced0c3280
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 1173fa067 P4D 1173fa067 PUD 1171b6067 PMD 1171dd067 PTE 0
 Oops: 0000 [#1] PREEMPT SMP
 CPU: 6 PID: 1810 Comm: cat Not tainted 5.13.0-rc5-test+ #61
 Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01
v03.03 07/14/2016
 RIP: 0010:strlen+0x0/0x20
 Code: f6 82 80 2a 0b a9 20 74 11 0f b6 50 01 48 83 c0 01 f6 82 80 2a 0b
a9 20 75 ef c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 <80> 3f 00 74
10 48 89 f8 48 83 c0 01 80 38 00 75 f7 48 29 f8 c3

 RSP: 0018:ffffbdbf81567b50 EFLAGS: 00010246
 RAX: 0000000000000003 RBX: ffff93815cdb3800 RCX: ffff9382401a22d0
 RDX: 0000000000000100 RSI: 0000000000000000 RDI: 00007f2ced0c3280
 RBP: 0000000000000100 R08: ffff9382409ff074 R09: ffffbdbf81567c98
 R10: ffff9382409ff074 R11: 0000000000000000 R12: ffff9382409ff074
 R13: 0000000000000001 R14: ffff93815a744f00 R15: 00007f2ced0c3280
 FS:  00007f2ced0f8580(0000) GS:ffff93825a800000(0000)
knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007f2ced0c3280 CR3: 0000000107069005 CR4: 00000000001706e0
 Call Trace:
  event_hist_trigger+0x463/0x5f0
  ? find_held_lock+0x32/0x90
  ? sched_clock_cpu+0xe/0xd0
  ? lock_release+0x155/0x440
  ? kernel_init_free_pages+0x6d/0x90
  ? preempt_count_sub+0x9b/0xd0
  ? kernel_init_free_pages+0x6d/0x90
  ? get_page_from_freelist+0x12c4/0x1680
  ? __rb_reserve_next+0xe5/0x460
  ? ring_buffer_lock_reserve+0x12a/0x3f0
  event_triggers_call+0x52/0xe0
  ftrace_syscall_enter+0x264/0x2c0
  syscall_trace_enter.constprop.0+0x1ee/0x210
  do_syscall_64+0x1c/0x80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Where it triggered a fault on strlen(key) where key was the filename.

The reason is that filename is a char * to user space, and the histogram
code just blindly dereferenced it, with obvious bad results.

I originally tried to use strncpy_from_user/kernel_nofault() but found
that there's other places that its dereferenced and not worth the effort.

Just do not allow "char *" to act like strings.

Link: https://lkml.kernel.org/r/20210715000206.025df9d2@rorschach.local.home

Cc: Ingo Molnar 
Cc: Andrew Morton 
Cc: Masami Hiramatsu 
Cc: Tzvetomir Stoyanov 
Cc: stable@vger.kernel.org
Acked-by: Namhyung Kim 
Acked-by: Tom Zanussi 
Fixes: 79e577cbce4c4 ("tracing: Support string type key properly")
Fixes: 5967bd5c4239 ("tracing: Let filter_assign_type() detect FILTER_PTR_STRING")
Signed-off-by: Steven Rostedt (VMware)

Merge tag 'trace-v5.14-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

2021-07-09T18:15:09+00:00

Pull tracing fix and cleanup from Steven Rostedt:
 "Tracing fix for histograms and a clean up in ftrace:

   - Fixed a bug that broke the .sym-offset modifier and added a test to
     make sure nothing breaks it again.

   - Replace a list_del/list_add() with a list_move()"

* tag 'trace-v5.14-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace: Use list_move instead of list_del/list_add
  tracing/selftests: Add tests to test histogram sym and sym-offset modifiers
  tracing/histograms: Fix parsing of "sym-offset" modifier

ftrace: Use list_move instead of list_del/list_add

2021-07-08T17:02:58+00:00

Using list_move() instead of list_del() + list_add().

Link: https://lkml.kernel.org/r/20210608031108.2820996-1-libaokun1@huawei.com

Reported-by: Hulk Robot 
Signed-off-by: Baokun Li 
Signed-off-by: Steven Rostedt (VMware)