ARC: perf: Accommodate big-endian CPU
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Message ID 20191022140411.10193-1-abrodkin@synopsys.com
State New
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Series
  • ARC: perf: Accommodate big-endian CPU
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Commit Message

Alexey Brodkin Oct. 22, 2019, 2:04 p.m. UTC
8-letter strings representing ARC perf events are stores in two
32-bit registers as ASCII characters like that: "IJMP", "IALL", "IJMPTAK" etc.

And the same order of bytes in the word is used regardless CPU endianness.

Which means in case of big-endian CPU core we need to swap bytes to get
the same order as if it was on little-endian CPU.

Otherwise we're seeing the following error message on boot:
------------------------->8----------------------
ARC perf        : 8 counters (32 bits), 40 conditions, [overflow IRQ support]
sysfs: cannot create duplicate filename '/devices/arc_pct/events/pmji'
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.2.18 #3
Stack Trace:
  arc_unwind_core+0xd4/0xfc
  dump_stack+0x64/0x80
  sysfs_warn_dup+0x46/0x58
  sysfs_add_file_mode_ns+0xb2/0x168
  create_files+0x70/0x2a0
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at kernel/events/core.c:12144 perf_event_sysfs_init+0x70/0xa0
Failed to register pmu: arc_pct, reason -17
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.2.18 #3
Stack Trace:
  arc_unwind_core+0xd4/0xfc
  dump_stack+0x64/0x80
  __warn+0x9c/0xd4
  warn_slowpath_fmt+0x22/0x2c
  perf_event_sysfs_init+0x70/0xa0
---[ end trace a75fb9a9837bd1ec ]---
------------------------->8----------------------

What happens here we're trying to register more than one raw perf event
with the same name "PMJI". Why? Because ARC perf events are 4 to 8 letters
and encoded into two 32-bit words. In this particular case we deal with 2
events:
 * "IJMP____" which counts all jump & branch instructions
 * "IJMPC___" which counts only conditional jumps & branches

Those strings are split in two 32-bit words this way "IJMP" + "____" &
"IJMP" + "C___" correspondingly. Now if we read them swapped due to CPU core
being big-endian then we read "PMJI" + "____" & "PMJI" + "___C".

And since we interpret read array of ASCII letters as a null-terminated string
on big-endian CPU we end up with 2 events of the same name "PMJI".

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: stable@vger.kernel.org
---
 arch/arc/kernel/perf_event.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Sasha Levin Oct. 26, 2019, 1:10 p.m. UTC | #1
Hi,

[This is an automated email]

This commit has been processed because it contains a -stable tag.
The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v5.3.7, v4.19.80, v4.14.150, v4.9.197, v4.4.197.

v5.3.7: Build OK!
v4.19.80: Failed to apply! Possible dependencies:
    0e956150fe09f ("ARC: perf: introduce Kernel PMU events support")
    14f81a91ad29a ("ARC: perf: trivial code cleanup")
    baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function")

v4.14.150: Failed to apply! Possible dependencies:
    0e956150fe09f ("ARC: perf: introduce Kernel PMU events support")
    14f81a91ad29a ("ARC: perf: trivial code cleanup")
    4d431290402c8 ("ARCv2: perf: tweak overflow interrupt")
    baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function")

v4.9.197: Failed to apply! Possible dependencies:
    0e956150fe09f ("ARC: perf: introduce Kernel PMU events support")
    14f81a91ad29a ("ARC: perf: trivial code cleanup")
    4d431290402c8 ("ARCv2: perf: tweak overflow interrupt")
    baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function")

v4.4.197: Failed to apply! Possible dependencies:
    05c74e5e53f6c ("bpf: add bpf_skb_load_bytes helper")
    0e956150fe09f ("ARC: perf: introduce Kernel PMU events support")
    14f81a91ad29a ("ARC: perf: trivial code cleanup")
    3379e0c3effa8 ("perf tools: Document the perf sysctls")
    45d8390c56bd2 ("bpf: hash: move select_bucket() out of htab's spinlock")
    538950a1b7527 ("soreuseport: setsockopt SO_ATTACH_REUSEPORT_[CE]BPF")
    568b329a02f75 ("perf: generalize perf_callchain")
    6591f1e6662dd ("bpf: hash: use atomic count")
    688ecfe602205 ("bpf: hash: use per-bucket spinlock")
    75925e1ad7f5a ("perf/x86: Optimize stack walk user accesses")
    781c53bc5d562 ("bpf: export helper function flags and reject invalid ones")
    824bd0ce6c7c4 ("bpf: introduce BPF_MAP_TYPE_PERCPU_HASH map")
    a10423b87a7ea ("bpf: introduce BPF_MAP_TYPE_PERCPU_ARRAY map")
    baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function")
    c5dfd78eb7985 ("perf core: Allow setting up max frame stack depth via sysctl")
    c6c33454072fc ("bpf: support ipv6 for bpf_skb_{set,get}_tunnel_key")
    cfbcf468454ab ("perf core: Pass max stack as a perf_callchain_entry context")
    d5a3b1f691865 ("bpf: introduce BPF_MAP_TYPE_STACK_TRACE")
    e32ea7e747271 ("soreuseport: fast reuseport UDP socket selection")
    ef456144da8ef ("soreuseport: define reuseport groups")
    f8ffad69c9f8b ("bpf: add skb_postpush_rcsum and fix dev_forward_skb occasions")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?
Alexey Brodkin Nov. 5, 2019, 7:52 p.m. UTC | #2
Hi Sasha, Greg,

> -----Original Message-----
> From: Sasha Levin <sashal@kernel.org>
> Sent: Saturday, October 26, 2019 4:11 PM
> To: Sasha Levin <sashal@kernel.org>; Alexey Brodkin <abrodkin@synopsys.com>; linux-snps-
> arc@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org; stable@vger.kernel.org; stable@vger.kernel.org
> Subject: Re: [PATCH] ARC: perf: Accommodate big-endian CPU
> 
> Hi,
> 
> [This is an automated email]
> 
> This commit has been processed because it contains a -stable tag.
> The stable tag indicates that it's relevant for the following trees: all
> 
> The bot has tested the following trees: v5.3.7, v4.19.80, v4.14.150, v4.9.197, v4.4.197.
> 
> v5.3.7: Build OK!
> v4.19.80: Failed to apply! Possible dependencies:
>     0e956150fe09f ("ARC: perf: introduce Kernel PMU events support")
>     14f81a91ad29a ("ARC: perf: trivial code cleanup")
>     baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function")
> v4.14.150: Failed to apply! Possible dependencies:
> v4.9.197: Failed to apply! Possible dependencies:
> v4.4.197: Failed to apply! Possible dependencies:

Indeed the clash is due to
commit baf9cc85ba01f ("ARC: perf: move HW events mapping to separate function") as tmp variable "j" was changed on "i". So that's a fixed hunk:
-------------------------------->8------------------------------
diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 8aec462d90fb..30f66b123541 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -490,8 +490,8 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
        /* loop thru all available h/w condition indexes */
        for (j = 0; j < cc_bcr.c; j++) {
                write_aux_reg(ARC_REG_CC_INDEX, j);
-               cc_name.indiv.word0 = read_aux_reg(ARC_REG_CC_NAME0);
-               cc_name.indiv.word1 = read_aux_reg(ARC_REG_CC_NAME1);
+               cc_name.indiv.word0 = le32_to_cpu(read_aux_reg(ARC_REG_CC_NAME0));
+               cc_name.indiv.word1 = le32_to_cpu(read_aux_reg(ARC_REG_CC_NAME1));

                /* See if it has been mapped to a perf event_id */
                for (i = 0; i < ARRAY_SIZE(arc_pmu_ev_hw_map); i++) {
-------------------------------->8------------------------------

Should I send a formal patch with it or it's OK for now?

-Alexey

Patch
diff mbox series

diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 861a8aea51f9..661fd842ea97 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -614,8 +614,8 @@  static int arc_pmu_device_probe(struct platform_device *pdev)
 	/* loop thru all available h/w condition indexes */
 	for (i = 0; i < cc_bcr.c; i++) {
 		write_aux_reg(ARC_REG_CC_INDEX, i);
-		cc_name.indiv.word0 = read_aux_reg(ARC_REG_CC_NAME0);
-		cc_name.indiv.word1 = read_aux_reg(ARC_REG_CC_NAME1);
+		cc_name.indiv.word0 = le32_to_cpu(read_aux_reg(ARC_REG_CC_NAME0));
+		cc_name.indiv.word1 = le32_to_cpu(read_aux_reg(ARC_REG_CC_NAME1));
 
 		arc_pmu_map_hw_event(i, cc_name.str);
 		arc_pmu_add_raw_event_attr(i, cc_name.str);