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ring-buffer: Fix for 6.12

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- Do not have boot-mapped buffers use CPU hotplug callbacks
 
   When a ring buffer is mapped to memory assigned at boot, it
   also splits it up evenly between the possible CPUs. But the
   allocation code still attached a CPU notifier callback to this
   ring buffer. When a CPU is added, the callback will happen and
   another per-cpu buffer is created for the ring buffer. But for
   boot mapped buffers, there is no room to add another one (as
   they were all created already). The result of calling the CPU
   hotplug notifier on a boot mapped ring buffer is unpredictable
   and could lead to a system crash. If the ring buffer is boot mapped
   simply do not attach the CPU notifier to it.
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Merge tag 'trace-ringbuffer-v6.12-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing fix from Steven Rostedt:
 "Ring-buffer fix: do not have boot-mapped buffers use CPU hotplug
  callbacks

  When a ring buffer is mapped to memory assigned at boot, it also
  splits it up evenly between the possible CPUs. But the allocation code
  still attached a CPU notifier callback to this ring buffer. When a CPU
  is added, the callback will happen and another per-cpu buffer is
  created for the ring buffer.

  But for boot mapped buffers, there is no room to add another one (as
  they were all created already). The result of calling the CPU hotplug
  notifier on a boot mapped ring buffer is unpredictable and could lead
  to a system crash.

  If the ring buffer is boot mapped simply do not attach the CPU
  notifier to it"

* tag 'trace-ringbuffer-v6.12-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Do not have boot mapped buffers hook to CPU hotplug
This commit is contained in:
Linus Torvalds 2024-10-10 12:25:32 -07:00
commit 0edab8d132
1 changed files with 6 additions and 3 deletions
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9
kernel/trace/ring_buffer.c
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@ -2337,9 +2337,12 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
if (!buffer->buffers[cpu])
goto fail_free_buffers;
ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
if (ret < 0)
goto fail_free_buffers;
/* If already mapped, do not hook to CPU hotplug */
if (!start) {
ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
if (ret < 0)
goto fail_free_buffers;
}
mutex_init(&buffer->mutex);