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ftrace: Fix preemption accounting for stacktrace filter command

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commit 11aff32439df6ca5b3b891b43032faf88f4a6a29 upstream.

The preemption count of the stacktrace filter command to trace ksys_read
is consistently incorrect:

$ echo ksys_read:stacktrace > set_ftrace_filter

   <...>-453     [004] ...1.    38.308956: <stack trace>
=> ksys_read
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

The root cause is that the trace framework disables preemption when
invoking the filter command callback in function_trace_probe_call:

   preempt_disable_notrace();
   probe_ops->func(ip, parent_ip, probe_opsbe->tr, probe_ops, probe->data);
   preempt_enable_notrace();

Use tracing_gen_ctx_dec() to account for the preempt_disable_notrace(),
which will output the correct preemption count:

$ echo ksys_read:stacktrace > set_ftrace_filter

   <...>-410     [006] .....    31.420396: <stack trace>
=> ksys_read
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

Cc: stable@vger.kernel.org
Fixes: 36590c50b2 ("tracing: Merge irqflags + preempt counter.")
Link: https://lore.kernel.org/20250512094246.1167956-2-dolinux.peng@gmail.com
Signed-off-by: pengdonglin <dolinux.peng@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
pengdonglin
2025-05-12 17:42:46 +08:00
committed by Greg Kroah-Hartman
parent fa75d941b1
commit 9d1216bf49
1 changed files with 1 additions and 5 deletions
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6
kernel/trace/trace_functions.c
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@@ -561,11 +561,7 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
static __always_inline void trace_stack(struct trace_array *tr)
{
unsigned int trace_ctx;
trace_ctx = tracing_gen_ctx();
__trace_stack(tr, trace_ctx, FTRACE_STACK_SKIP);
__trace_stack(tr, tracing_gen_ctx_dec(), FTRACE_STACK_SKIP);
}
static void