Patch "samples/bpf: fix bio latency check with tracepoint" has been added to the 6.5-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    samples/bpf: fix bio latency check with tracepoint

to the 6.5-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     samples-bpf-fix-bio-latency-check-with-tracepoint.patch
and it can be found in the queue-6.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ae06b8c414044798717c250d77168ec30fe20d7d
Author: Daniel T. Lee <danieltimlee@xxxxxxxxx>
Date:   Fri Aug 18 18:01:16 2023 +0900

    samples/bpf: fix bio latency check with tracepoint
    
    [ Upstream commit 92632115fb57ff9e368f256913e96d6fd5abf5ab ]
    
    Recently, a new tracepoint for the block layer, specifically the
    block_io_start/done tracepoints, was introduced in commit 5a80bd075f3b
    ("block: introduce block_io_start/block_io_done tracepoints").
    
    Previously, the kprobe entry used for this purpose was quite unstable
    and inherently broke relevant probes [1]. Now that a stable tracepoint
    is available, this commit replaces the bio latency check with it.
    
    One of the changes made during this replacement is the key used for the
    hash table. Since 'struct request' cannot be used as a hash key, the
    approach taken follows that which was implemented in bcc/biolatency [2].
    (uses dev:sector for the key)
    
    [1]: https://github.com/iovisor/bcc/issues/4261
    [2]: https://github.com/iovisor/bcc/pull/4691
    
    Fixes: 450b7879e345 ("block: move blk_account_io_{start,done} to blk-mq.c")
    Signed-off-by: Daniel T. Lee <danieltimlee@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20230818090119.477441-7-danieltimlee@xxxxxxxxx
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/samples/bpf/tracex3_kern.c b/samples/bpf/tracex3_kern.c
index bde6591cb20c5..af235bd6615b1 100644
--- a/samples/bpf/tracex3_kern.c
+++ b/samples/bpf/tracex3_kern.c
@@ -11,6 +11,12 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
+struct start_key {
+	dev_t dev;
+	u32 _pad;
+	sector_t sector;
+};
+
 struct {
 	__uint(type, BPF_MAP_TYPE_HASH);
 	__type(key, long);
@@ -18,16 +24,17 @@ struct {
 	__uint(max_entries, 4096);
 } my_map SEC(".maps");
 
-/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
- * example will no longer be meaningful
- */
-SEC("kprobe/blk_mq_start_request")
-int bpf_prog1(struct pt_regs *ctx)
+/* from /sys/kernel/tracing/events/block/block_io_start/format */
+SEC("tracepoint/block/block_io_start")
+int bpf_prog1(struct trace_event_raw_block_rq *ctx)
 {
-	long rq = PT_REGS_PARM1(ctx);
 	u64 val = bpf_ktime_get_ns();
+	struct start_key key = {
+		.dev = ctx->dev,
+		.sector = ctx->sector
+	};
 
-	bpf_map_update_elem(&my_map, &rq, &val, BPF_ANY);
+	bpf_map_update_elem(&my_map, &key, &val, BPF_ANY);
 	return 0;
 }
 
@@ -49,21 +56,26 @@ struct {
 	__uint(max_entries, SLOTS);
 } lat_map SEC(".maps");
 
-SEC("kprobe/__blk_account_io_done")
-int bpf_prog2(struct pt_regs *ctx)
+/* from /sys/kernel/tracing/events/block/block_io_done/format */
+SEC("tracepoint/block/block_io_done")
+int bpf_prog2(struct trace_event_raw_block_rq *ctx)
 {
-	long rq = PT_REGS_PARM1(ctx);
+	struct start_key key = {
+		.dev = ctx->dev,
+		.sector = ctx->sector
+	};
+
 	u64 *value, l, base;
 	u32 index;
 
-	value = bpf_map_lookup_elem(&my_map, &rq);
+	value = bpf_map_lookup_elem(&my_map, &key);
 	if (!value)
 		return 0;
 
 	u64 cur_time = bpf_ktime_get_ns();
 	u64 delta = cur_time - *value;
 
-	bpf_map_delete_elem(&my_map, &rq);
+	bpf_map_delete_elem(&my_map, &key);
 
 	/* the lines below are computing index = log10(delta)*10
 	 * using integer arithmetic