Re: [PATCH 4.19] perf/x86/intel/pt: Fix buffer full but size is 0 case

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 5b590160d2cf776b304eb054afafea2bd55e3620


Status in newer kernel trees:
6.12.y | Present (different SHA1: bd0081617661)
6.11.y | Present (different SHA1: 549225e02e9b)
6.6.y | Present (different SHA1: 1488d93e3e1f)
6.1.y | Present (different SHA1: bda8868213ee)
5.15.y | Present (different SHA1: 1b843f820f7a)
5.10.y | Present (different SHA1: b243226da582)
5.4.y | Not found
4.19.y | Not found

Note: The patch differs from the upstream commit:
---
1:  5b590160d2cf7 ! 1:  787e984867a5b perf/x86/intel/pt: Fix buffer full but size is 0 case
    @@ Metadata
      ## Commit message ##
         perf/x86/intel/pt: Fix buffer full but size is 0 case
     
    +    commit 5b590160d2cf776b304eb054afafea2bd55e3620 upstream.
    +
         If the trace data buffer becomes full, a truncated flag [T] is reported
         in PERF_RECORD_AUX.  In some cases, the size reported is 0, even though
         data must have been added to make the buffer full.
    @@ Commit message
         Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
         Cc: stable@vger.kernel.org
         Link: https://lkml.kernel.org/r/20241022155920.17511-2-adrian.hunter@intel.com
    +    Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
     
      ## arch/x86/events/intel/pt.c ##
     @@ arch/x86/events/intel/pt.c: static void pt_buffer_advance(struct pt_buffer *buf)
    @@ arch/x86/events/intel/pt.c: static void pt_buffer_advance(struct pt_buffer *buf)
      
     +	buf->wrapped = false;
     +
    - 	if (buf->single) {
    - 		local_set(&buf->data_size, buf->output_off);
    - 		return;
    + 	/* offset of the first region in this table from the beginning of buf */
    + 	base = buf->cur->offset + buf->output_off;
    + 
     @@ arch/x86/events/intel/pt.c: static void pt_update_head(struct pt *pt)
      	} else {
      		old = (local64_xchg(&buf->head, base) &
    @@ arch/x86/events/intel/pt.c: static void pt_update_head(struct pt *pt)
     
      ## arch/x86/events/intel/pt.h ##
     @@ arch/x86/events/intel/pt.h: struct pt_pmu {
    +  * @lost:	if data was lost/truncated
       * @head:	logical write offset inside the buffer
       * @snapshot:	if this is for a snapshot/overwrite counter
    -  * @single:	use Single Range Output instead of ToPA
     + * @wrapped:	buffer advance wrapped back to the first topa table
    -  * @stop_pos:	STOP topa entry index
    -  * @intr_pos:	INT topa entry index
    -  * @stop_te:	STOP topa entry pointer
    +  * @stop_pos:	STOP topa entry in the buffer
    +  * @intr_pos:	INT topa entry in the buffer
    +  * @data_pages:	array of pages from perf
     @@ arch/x86/events/intel/pt.h: struct pt_buffer {
    + 	local_t			data_size;
      	local64_t		head;
      	bool			snapshot;
    - 	bool			single;
     +	bool			wrapped;
    - 	long			stop_pos, intr_pos;
    - 	struct topa_entry	*stop_te, *intr_te;
    + 	unsigned long		stop_pos, intr_pos;
      	void			**data_pages;
    + 	struct topa_entry	*topa_index[0];
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-4.19.y       |  Success    |  Success   |