49 lines
1.6 KiB
Diff
49 lines
1.6 KiB
Diff
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From fc245dfe9dabbd77e3adbf89a45aaab0cb1552fd Mon Sep 17 00:00:00 2001
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From: Mark Drayton <mark@markdrayton.info>
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Date: Wed, 19 Sep 2018 16:41:49 -0700
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Subject: [PATCH] biolatency: Fix --disks bpf_probe_read() (#1980)
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bpf_probe_read()'s third argument is no longer rewritten. Instead, use a
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temporary variable (like #1973) to avoid a memory access error.
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Before:
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```
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$ sudo biolatency -D 1
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bpf: Failed to load program: Permission denied
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0: (79) r1 = *(u64 *)(r1 +112)
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1: (7b) *(u64 *)(r10 -8) = r1
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[..]
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R1 invalid mem access 'inv'
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HINT: The invalid mem access 'inv' error can happen if you try to
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dereference memory without first using bpf_probe_read() to copy it to
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the BPF stack. Sometimes the bpf_probe_read is automatic by the bcc
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rewriter, other times you'll need to be explicit.
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```
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After, works as expected.
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---
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tools/biolatency.py | 5 +++--
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1 file changed, 3 insertions(+), 2 deletions(-)
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diff --git a/tools/biolatency.py b/tools/biolatency.py
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index 49ee7cf..3879af1 100755
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--- a/tools/biolatency.py
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+++ b/tools/biolatency.py
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@@ -99,8 +99,9 @@ int trace_req_completion(struct pt_regs *ctx, struct request *req)
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'BPF_HISTOGRAM(dist, disk_key_t);')
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bpf_text = bpf_text.replace('STORE',
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'disk_key_t key = {.slot = bpf_log2l(delta)}; ' +
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- 'bpf_probe_read(&key.disk, sizeof(key.disk), ' +
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- 'req->rq_disk->disk_name); dist.increment(key);')
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+ 'void *__tmp = (void *)req->rq_disk->disk_name; ' +
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+ 'bpf_probe_read(&key.disk, sizeof(key.disk), __tmp); ' +
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+ 'dist.increment(key);')
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else:
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bpf_text = bpf_text.replace('STORAGE', 'BPF_HISTOGRAM(dist);')
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bpf_text = bpf_text.replace('STORE',
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--
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2.19.2
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