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cbe08bcbbe
linux_dsm_epyc7002/kernel/trace
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Elazar Leibovich cbe08bcbbe tracing: Fix partial reading of trace event's id file 
When reading only part of the id file, the ppos isn't tracked correctly.
This is taken care by simple_read_from_buffer.

Reading a single byte, and then the next byte would result EOF.

While this seems like not a big deal, this breaks abstractions that
reads information from files unbuffered. See for example
https://github.com/golang/go/issues/29399

This code was mentioned as problematic in
commit cd458ba9d5
("tracing: Do not (ab)use trace_seq in event_id_read()")

An example C code that show this bug is:

  #include <stdio.h>
  #include <stdint.h>

  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <unistd.h>

  int main(int argc, char **argv) {
    if (argc < 2)
      return 1;
    int fd = open(argv[1], O_RDONLY);
    char c;
    read(fd, &c, 1);
    printf("First  %c\n", c);
    read(fd, &c, 1);
    printf("Second %c\n", c);
  }

Then run with, e.g.

  sudo ./a.out /sys/kernel/debug/tracing/events/tcp/tcp_set_state/id

You'll notice you're getting the first character twice, instead of the
first two characters in the id file.

Link: http://lkml.kernel.org/r/20181231115837.4932-1-elazar@lightbitslabs.com

Cc: Orit Wasserman <orit.was@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 23725aeeab ("ftrace: provide an id file for each event")
Signed-off-by: Elazar Leibovich <elazar@lightbitslabs.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2019-05-08 12:15:12 -04:00
..
blktrace.c blkcg: annotate implicit fall through 2019-03-13 14:31:12 -06:00
bpf_trace.c Merge branch 'linus' into perf/core, to pick up fixes 2019-02-28 08:27:17 +01:00
fgraph.c tracing: Fix ftrace_graph_get_ret_stack() to use task and not current 2018-12-22 08:21:03 -05:00
ftrace_internal.h ftrace: Create new ftrace_internal.h header 2018-12-08 20:54:06 -05:00
ftrace.c tracing: Eliminate const char[] auto variables 2019-05-08 12:15:12 -04:00
Kconfig kbuild: compute false-positive -Wmaybe-uninitialized cases in Kconfig 2019-02-27 21:43:20 +09:00
Makefile tracing: Add unified dynamic event framework 2018-12-08 20:54:09 -05:00
power-traces.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
preemptirq_delay_test.c tracing: Use trace_clock_local() for looping in preemptirq_delay_test.c 2018-10-17 15:35:33 -04:00
ring_buffer_benchmark.c ring-buffer: Fix mispelling of Calculate 2019-05-08 12:15:12 -04:00
ring_buffer.c ring-buffer: Fix ring buffer size in rb_write_something() 2019-04-02 18:24:06 -04:00
rpm-traces.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_benchmark.c rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() 2018-05-15 10:27:29 -07:00
trace_benchmark.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00
trace_branch.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_clock.c tracing: Add SPDX License format tags to tracing files 2018-08-16 19:08:06 -04:00
trace_dynevent.c tracing: initialize variable in create_dyn_event() 2019-03-26 08:35:36 -04:00
trace_dynevent.h tracing: Add unified dynamic event framework 2018-12-08 20:54:09 -05:00
trace_entries.h tracing: Change the function format to display function names by perf 2019-02-11 14:53:43 -05:00
trace_event_perf.c tracing/perf: Use strndup_user() instead of buggy open-coded version 2019-02-21 10:35:10 -05:00
trace_events_filter_test.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00
trace_events_filter.c tracing: Fix white space issues in parse_pred() function 2019-05-08 12:15:12 -04:00
trace_events_hist.c tracing: Have the error logs show up in the proper instances 2019-04-08 09:22:44 -04:00
trace_events_trigger.c tracing: Add trace_array parameter to create_event_filter() 2019-04-08 09:22:28 -04:00
trace_events.c tracing: Fix partial reading of trace event's id file 2019-05-08 12:15:12 -04:00
trace_export.c tracing: Add trigger file for trace_markers tracefs/ftrace/print 2018-05-29 08:28:53 -04:00
trace_functions_graph.c tracing: Put a margin between flags and duration for wakeup tracers 2019-02-06 11:56:19 -05:00
trace_functions.c tracing: Update stack trace skipping for ORC unwinder 2018-01-23 15:57:00 -05:00
trace_hwlat.c tracing: Add SPDX License format tags to tracing files 2018-08-16 19:08:06 -04:00
trace_irqsoff.c The biggest change for this release is in the histogram code. 2019-03-11 17:01:32 -07:00
trace_kdb.c tracing: kdb: Allow ftdump to skip all but the last few entries 2019-05-02 21:32:55 -04:00
trace_kprobe_selftest.c selftest/ftrace: Move kprobe selftest function to separate compile unit 2018-07-30 18:41:04 -04:00
trace_kprobe_selftest.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00
trace_kprobe.c tracing: Use tracing error_log with probe events 2019-04-02 18:24:07 -04:00
trace_mmiotrace.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_nop.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_output.c tracing: Simplify printf'ing in seq_print_sym 2018-12-22 08:21:06 -05:00
trace_output.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00
trace_preemptirq.c kprobes: Prohibit probing on hardirq tracers 2019-02-13 08:16:40 +01:00
trace_printk.c tracing: Trivia spelling fix containerof() -> container_of() 2018-09-26 12:21:00 +03:00
trace_probe_tmpl.h tracing: probeevent: Do not accumulate on ret variable 2019-05-08 12:15:11 -04:00
trace_probe.c tracing: probeevent: Fix to make the type of $comm string 2019-05-08 12:15:11 -04:00
trace_probe.h tracing: uprobes: Re-enable $comm support for uprobe events 2019-05-08 12:15:11 -04:00
trace_sched_switch.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_sched_wakeup.c tracing: Add conditional snapshot 2019-02-20 13:51:06 -05:00
trace_selftest_dynamic.c ftrace: Mark function tracer test functions noinline/noclone 2018-01-23 15:57:29 -05:00
trace_selftest.c function_graph: Have selftest also emulate tr->reset() as it did with tr->init() 2019-04-21 19:46:56 -04:00
trace_seq.c tracing: Add SPDX License format tags to tracing files 2018-08-16 19:08:06 -04:00
trace_stack.c tracing: Use the return of str_has_prefix() to remove open coded numbers 2018-12-22 22:52:30 -05:00
trace_stat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace_stat.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00
trace_syscalls.c Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
trace_uprobe.c tracing: uprobes: Re-enable $comm support for uprobe events 2019-05-08 12:15:11 -04:00
trace.c tracing: Allow RCU to run between postponed startup tests 2019-05-08 12:15:12 -04:00
trace.h tracing: Add trace_total_entries() / trace_total_entries_cpu() 2019-05-02 21:32:31 -04:00
tracing_map.c tracing: Add SPDX License format tags to tracing files 2018-08-16 19:08:06 -04:00
tracing_map.h tracing: Fix SPDX format headers to use C++ style comments 2018-08-16 19:08:06 -04:00