linux-stable/kernel
Steven Rostedt (VMware) bf470f0515 tracing: Fix histogram code when expression has same var as value
commit 8bcebc77e8 upstream.

While working on a tool to convert SQL syntex into the histogram language of
the kernel, I discovered the following bug:

 # echo 'first u64 start_time u64 end_time pid_t pid u64 delta' >> synthetic_events
 # echo 'hist:keys=pid:start=common_timestamp' > events/sched/sched_waking/trigger
 # echo 'hist:keys=next_pid:delta=common_timestamp-$start,start2=$start:onmatch(sched.sched_waking).trace(first,$start2,common_timestamp,next_pid,$delta)' > events/sched/sched_switch/trigger

Would not display any histograms in the sched_switch histogram side.

But if I were to swap the location of

  "delta=common_timestamp-$start" with "start2=$start"

Such that the last line had:

 # echo 'hist:keys=next_pid:start2=$start,delta=common_timestamp-$start:onmatch(sched.sched_waking).trace(first,$start2,common_timestamp,next_pid,$delta)' > events/sched/sched_switch/trigger

The histogram works as expected.

What I found out is that the expressions clear out the value once it is
resolved. As the variables are resolved in the order listed, when
processing:

  delta=common_timestamp-$start

The $start is cleared. When it gets to "start2=$start", it errors out with
"unresolved symbol" (which is silent as this happens at the location of the
trace), and the histogram is dropped.

When processing the histogram for variable references, instead of adding a
new reference for a variable used twice, use the same reference. That way,
not only is it more efficient, but the order will no longer matter in
processing of the variables.

From Tom Zanussi:

 "Just to clarify some more about what the problem was is that without
  your patch, we would have two separate references to the same variable,
  and during resolve_var_refs(), they'd both want to be resolved
  separately, so in this case, since the first reference to start wasn't
  part of an expression, it wouldn't get the read-once flag set, so would
  be read normally, and then the second reference would do the read-once
  read and also be read but using read-once.  So everything worked and
  you didn't see a problem:

   from: start2=$start,delta=common_timestamp-$start

  In the second case, when you switched them around, the first reference
  would be resolved by doing the read-once, and following that the second
  reference would try to resolve and see that the variable had already
  been read, so failed as unset, which caused it to short-circuit out and
  not do the trigger action to generate the synthetic event:

   to: delta=common_timestamp-$start,start2=$start

  With your patch, we only have the single resolution which happens
  correctly the one time it's resolved, so this can't happen."

Link: https://lore.kernel.org/r/20200116154216.58ca08eb@gandalf.local.home

Cc: stable@vger.kernel.org
Fixes: 067fe038e7 ("tracing: Add variable reference handling to hist triggers")
Reviewed-by: Tom Zanuss <zanussi@kernel.org>
Tested-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-01-29 16:45:26 +01:00
..
bpf xdp: Fix cleanup on map free for devmap_hash map type 2020-01-26 10:01:08 +01:00
cgroup cgroup: freezer: don't change task and cgroups status unnecessarily 2019-12-31 16:45:06 +01:00
configs
debug kgdb: don't use a notifier to enter kgdb at panic; call directly 2019-09-25 17:51:40 -07:00
dma dma-direct: don't check swiotlb=force in dma_direct_map_resource 2020-01-26 10:01:08 +01:00
events perf: Correctly handle failed perf_get_aux_event() 2020-01-23 08:22:33 +01:00
gcov um: Enable CONFIG_CONSTRUCTORS 2019-09-15 21:37:13 +02:00
irq irq/irqdomain: Update __irq_domain_alloc_fwnode() function documentation 2019-11-05 00:48:26 +01:00
livepatch livepatch: Nullify obj->mod in klp_module_coming()'s error path 2019-08-19 13:03:37 +02:00
locking locking/lockdep: Fix buffer overrun problem in stack_trace[] 2020-01-23 08:22:39 +01:00
power PM: hibernate: fix crashes with init_on_free=1 2020-01-29 16:45:25 +01:00
printk Merge branch 'for-5.4' into for-linus 2019-09-16 12:54:25 +02:00
rcu rcu: Fix uninitialized variable in nocb_gp_wait() 2020-01-26 10:01:05 +01:00
sched sched/cpufreq: Move the cfs_rq_util_change() call to cpufreq_update_util() 2020-01-26 10:01:08 +01:00
time tick/sched: Annotate lockless access to last_jiffies_update 2020-01-23 08:22:55 +01:00
trace tracing: Fix histogram code when expression has same var as value 2020-01-29 16:45:26 +01:00
.gitignore Provide in-kernel headers to make extending kernel easier 2019-04-29 16:48:03 +02:00
acct.c acct_on(): don't mess with freeze protection 2019-04-04 21:04:13 -04:00
async.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
audit.c audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
audit.h audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
audit_fsnotify.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
audit_tree.c fsnotify: switch send_to_group() and ->handle_event to const struct qstr * 2019-04-26 13:51:03 -04:00
audit_watch.c audit_get_nd(): don't unlock parent too early 2019-11-10 11:56:55 -05:00
auditfilter.c audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
auditsc.c audit: enforce op for string fields 2019-05-28 17:46:43 -04:00
backtracetest.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
bounds.c
capability.c LSM: add SafeSetID module that gates setid calls 2019-01-25 11:22:43 -08:00
compat.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
configs.c kernel/configs: Replace GPL boilerplate code with SPDX identifier 2019-07-30 18:34:15 +02:00
context_tracking.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cpu.c cpu/SMT: Fix x86 link error without CONFIG_SYSFS 2020-01-23 08:22:36 +01:00
cpu_pm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 282 2019-06-05 17:36:37 +02:00
crash_core.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 230 2019-06-19 17:09:06 +02:00
crash_dump.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cred.c keys: Fix request_key() cache 2020-01-17 19:48:42 +01:00
delayacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
dma.c
elfcore.c kernel/elfcore.c: include proper prototypes 2019-09-25 17:51:39 -07:00
exec_domain.c
exit.c exit: panic before exit_mm() on global init exit 2020-01-09 10:20:01 +01:00
extable.c extable: Add function to search only kernel exception table 2019-08-21 22:23:48 +10:00
fail_function.c fail_function: no need to check return value of debugfs_create functions 2019-06-03 15:49:06 +02:00
fork.c clone3: ensure copy_thread_tls is implemented 2020-01-14 20:08:35 +01:00
freezer.c Revert "libata, freezer: avoid block device removal while system is frozen" 2019-10-06 09:11:37 -06:00
futex.c futex: Prevent exit livelock 2019-11-29 10:10:14 +01:00
gen_kheaders.sh kheaders: substituting --sort in archive creation 2019-10-17 09:08:19 +09:00
groups.c
hung_task.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
iomem.c mm/nvdimm: add is_ioremap_addr and use that to check ioremap address 2019-07-12 11:05:40 -07:00
irq_work.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
jump_label.c jump_label: Don't warn on __exit jump entries 2019-08-29 15:10:10 +01:00
kallsyms.c kallsyms: Don't let kallsyms_lookup_size_offset() fail on retrieving the first symbol 2019-08-27 16:19:56 +01:00
kcmp.c
Kconfig.freezer treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.hz treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.locks treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.preempt sched/rt, Kconfig: Unbreak def/oldconfig with CONFIG_PREEMPT=y 2019-07-22 18:05:11 +02:00
kcov.c kcov: convert kcov.refcount to refcount_t 2019-03-07 18:32:02 -08:00
kexec.c kexec_load: Disable at runtime if the kernel is locked down 2019-08-19 21:54:15 -07:00
kexec_core.c kexec: bail out upon SIGKILL when allocating memory. 2019-09-25 17:51:40 -07:00
kexec_elf.c kexec_elf: support 32 bit ELF files 2019-09-06 23:58:44 +02:00
kexec_file.c Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
kexec_internal.h
kheaders.c kheaders: Move from proc to sysfs 2019-05-24 20:16:01 +02:00
kmod.c
kprobes.c Tracing updates: 2019-09-20 11:19:48 -07:00
ksysfs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 170 2019-05-30 11:26:39 -07:00
kthread.c kthread: make __kthread_queue_delayed_work static 2019-10-16 09:20:58 -07:00
latencytop.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
Makefile Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2019-09-27 19:37:27 -07:00
module-internal.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
module.c kernel/module.c: wakeup processes in module_wq on module unload 2020-01-09 10:20:02 +01:00
module_signature.c MODSIGN: Export module signature definitions 2019-08-05 18:39:56 -04:00
module_signing.c MODSIGN: Export module signature definitions 2019-08-05 18:39:56 -04:00
notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
nsproxy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
padata.c padata: remove cpu_index from the parallel_queue 2019-09-13 21:15:41 +10:00
panic.c panic: ensure preemption is disabled during panic() 2019-10-07 15:47:19 -07:00
params.c lockdown: Lock down module params that specify hardware parameters (eg. ioport) 2019-08-19 21:54:16 -07:00
pid.c kernel/pid.c: convert struct pid count to refcount_t 2019-07-16 19:23:24 -07:00
pid_namespace.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
profile.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
ptrace.c ptrace: reintroduce usage of subjective credentials in ptrace_has_cap() 2020-01-23 08:22:36 +01:00
range.c
reboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
relay.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 13:27:20 -07:00
resource.c mm/memory_hotplug.c: use PFN_UP / PFN_DOWN in walk_system_ram_range() 2019-09-24 15:54:09 -07:00
rseq.c signal: Remove task parameter from force_sig 2019-05-27 09:36:28 -05:00
seccomp.c seccomp: Check that seccomp_notif is zeroed out by the user 2020-01-09 10:19:57 +01:00
signal.c cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace_stop() 2019-10-11 08:39:57 -07:00
smp.c smp: Warn on function calls from softirq context 2019-07-20 11:27:16 +02:00
smpboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
smpboot.h
softirq.c Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-07-08 11:01:13 -07:00
stackleak.c
stacktrace.c stacktrace: Don't skip first entry on noncurrent tasks 2019-11-04 21:19:25 +01:00
stop_machine.c stop_machine: Avoid potential race behaviour 2019-10-17 12:47:12 +02:00
sys.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-09-17 12:35:15 -07:00
sys_ni.c arch: handle arches who do not yet define clone3 2019-06-21 01:54:53 +02:00
sysctl.c kernel: sysctl: make drop_caches write-only 2020-01-04 19:18:32 +01:00
sysctl_binary.c kernel/sysctl: add panic_print into sysctl 2019-01-04 13:13:47 -08:00
task_work.c
taskstats.c taskstats: fix data-race 2020-01-09 10:19:54 +01:00
test_kprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
torture.c torture: Remove exporting of internal functions 2019-08-01 14:30:22 -07:00
tracepoint.c The main changes in this release include: 2019-07-18 11:51:00 -07:00
tsacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
ucount.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
uid16.c
uid16.h
umh.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
up.c smp: Remove smp_call_function() and on_each_cpu() return values 2019-06-23 14:26:26 +02:00
user-return-notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
user.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
user_namespace.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
utsname.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
utsname_sysctl.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
watchdog.c watchdog: Mark watchdog_hrtimer to expire in hard interrupt context 2019-08-01 20:51:20 +02:00
watchdog_hld.c kernel/watchdog_hld.c: hard lockup message should end with a newline 2019-04-19 09:46:05 -07:00
workqueue.c workqueue: Add RCU annotation for pwq list walk 2020-01-26 10:01:07 +01:00
workqueue_internal.h sched/core, workqueues: Distangle worker accounting from rq lock 2019-04-16 16:55:15 +02:00