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tracing: Reset last-boot buffers when reading out all cpu buffers

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Reset the last-boot ring buffers when read() reads out all cpu
buffers through trace_pipe/trace_pipe_raw. This prevents ftrace to
unwind ring buffer read pointer next boot.

Note that this resets only when all per-cpu buffers are empty, and
read via read(2) syscall. For example, if you read only one of the
per-cpu trace_pipe, it does not reset it. Also, reading buffer by
splice(2) syscall does not reset because some data in the reader
(the last) page.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/174792929202.496143.8184644221859580999.stgit@mhiramat.tok.corp.google.com
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu (Google) 2025-05-23 00:54:52 +09:00 • committed by Steven Rostedt (Google)
parent c2a0831142
commit 32dc004252
1 changed files with 22 additions and 0 deletions
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22
kernel/trace/trace.c
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@ -6610,6 +6610,22 @@ static int tracing_wait_pipe(struct file *filp)
return 1;
}
static bool update_last_data_if_empty(struct trace_array *tr)
{
if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
return false;
if (!ring_buffer_empty(tr->array_buffer.buffer))
return false;
/*
* If the buffer contains the last boot data and all per-cpu
* buffers are empty, reset it from the kernel side.
*/
update_last_data(tr);
return true;
}
/*
* Consumer reader.
*/
@ -6641,6 +6657,9 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
}
waitagain:
if (update_last_data_if_empty(iter->tr))
return 0;
sret = tracing_wait_pipe(filp);
if (sret <= 0)
return sret;
@ -8167,6 +8186,9 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
if (ret < 0) {
if (trace_empty(iter) && !iter->closed) {
if (update_last_data_if_empty(iter->tr))
return 0;
if ((filp->f_flags & O_NONBLOCK))
return -EAGAIN;