git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 7c339fb4d8577792378136c15fde773cfb863cb8 Mon Sep 17 00:00:00 2001
   2 From: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
   3 Date: Wed, 26 Apr 2023 14:20:23 +0800
   4 Subject: ring-buffer: Ensure proper resetting of atomic variables in ring_buffer_reset_online_cpus
   5
   6 From: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
   7
   8 commit 7c339fb4d8577792378136c15fde773cfb863cb8 upstream.
   9
  10 In ring_buffer_reset_online_cpus, the buffer_size_kb write operation
  11 may permanently fail if the cpu_online_mask changes between two
  12 for_each_online_buffer_cpu loops. The number of increases and decreases
  13 on both cpu_buffer->resize_disabled and cpu_buffer->record_disabled may be
  14 inconsistent, causing some CPUs to have non-zero values for these atomic
  15 variables after the function returns.
  16
  17 This issue can be reproduced by "echo 0 > trace" while hotplugging cpu.
  18 After reproducing success, we can find out buffer_size_kb will not be
  19 functional anymore.
  20
  21 To prevent leaving 'resize_disabled' and 'record_disabled' non-zero after
  22 ring_buffer_reset_online_cpus returns, we ensure that each atomic variable
  23 has been set up before atomic_sub() to it.
  24
  25 Link: https://lore.kernel.org/linux-trace-kernel/20230426062027.17451-1-Tze-nan.Wu@mediatek.com
  26
  27 Cc: stable@vger.kernel.org
  28 Cc: <mhiramat@kernel.org>
  29 Cc: npiggin@gmail.com
  30 Fixes: b23d7a5f4a07 ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
  31 Reviewed-by: Cheng-Jui Wang <cheng-jui.wang@mediatek.com>
  32 Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
  33 Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
  34 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  35 ---
  36  kernel/trace/ring_buffer.c |   16 +++++++++++++---
  37  1 file changed, 13 insertions(+), 3 deletions(-)
  38
  39 --- a/kernel/trace/ring_buffer.c
  40 +++ b/kernel/trace/ring_buffer.c
  41 @@ -5333,6 +5333,9 @@ void ring_buffer_reset_cpu(struct trace_
  42  }
  43  EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
  44
  45 +/* Flag to ensure proper resetting of atomic variables */
  46 +#define RESET_BIT      (1 << 30)
  47 +
  48  /**
  49   * ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
  50   * @buffer: The ring buffer to reset a per cpu buffer of
  51 @@ -5349,20 +5352,27 @@ void ring_buffer_reset_online_cpus(struc
  52         for_each_online_buffer_cpu(buffer, cpu) {
  53                 cpu_buffer = buffer->buffers[cpu];
  54
  55 -               atomic_inc(&cpu_buffer->resize_disabled);
  56 +               atomic_add(RESET_BIT, &cpu_buffer->resize_disabled);
  57                 atomic_inc(&cpu_buffer->record_disabled);
  58         }
  59
  60         /* Make sure all commits have finished */
  61         synchronize_rcu();
  62
  63 -       for_each_online_buffer_cpu(buffer, cpu) {
  64 +       for_each_buffer_cpu(buffer, cpu) {
  65                 cpu_buffer = buffer->buffers[cpu];
  66
  67 +               /*
  68 +                * If a CPU came online during the synchronize_rcu(), then
  69 +                * ignore it.
  70 +                */
  71 +               if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT))
  72 +                       continue;
  73 +
  74                 reset_disabled_cpu_buffer(cpu_buffer);
  75
  76                 atomic_dec(&cpu_buffer->record_disabled);
  77 -               atomic_dec(&cpu_buffer->resize_disabled);
  78 +               atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
  79         }
  80
  81         mutex_unlock(&buffer->mutex);