linux-kernel - [PATCH] perf trace: Fix perf trace tracing itself, creating feedback loops

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Message-ID: <20241024174242.2816126-1-howardchu95@gmail.com>
Date: Thu, 24 Oct 2024 10:42:42 -0700
From: Howard Chu <howardchu95@...il.com>
To: acme@...nel.org
Cc: namhyung@...nel.org,
	irogers@...gle.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Howard Chu <howardchu95@...il.com>
Subject: [PATCH] perf trace: Fix perf trace tracing itself, creating feedback loops

Currently when tracing system-wide, perf trace will trace itself,
creating feedback loops. This patch fixes this problem by setting the
correct BPF map for filtering pids.

Before (here perf/2807067 is the tracing process itself):

perf $ ./perf trace -e write --max-events=10
     0.000 ( 0.007 ms): tmux: server/2299109 write(fd: 4, buf: \17, count: 1)                                      = 1 (systemd)
     0.060 (         ): perf/2807067 write(fd: 2, buf:      0.000 , count: 11)                          ...
     0.072 (         ): perf/2807067 write(fd: 2, buf: (, count: 1)                                     ...
     0.085 (         ): perf/2807067 write(fd: 2, buf:  0.007 ms, count: 9)                             ...
     0.089 (         ): perf/2807067 write(fd: 2, buf: ): , count: 3)                                   ...
     0.094 (         ): perf/2807067 write(fd: 2, buf: tmux: server/, count: 13)                        ...
     0.099 (         ): perf/2807067 write(fd: 2, buf: 2299109 , count: 8)                              ...
     0.103 (         ): perf/2807067 write(fd: 2, buf: write(fd: 4, buf: \17, count: 1, count: 31)      ...
     0.108 (         ): perf/2807067 write(fd: 2, buf: )                               , count: 41)     ...
     0.113 (         ): perf/2807067 write(fd: 2, buf: 1, count: 1)                                     ...

After:

perf $ ./perf trace -e write --max-events=10
     0.000 ( 0.030 ms): sshd/2725386 write(fd: 4, buf: r\148\133\163\17\167\194\172bF\231\192\227\194\215\251kBLE\167(\10WY\22\138^\233\28\248\249, count: 36) = 36 (idle_inject/3)
     0.622 ( 0.019 ms): sshd/2725386 write(fd: 4, buf: \177"\251\159\244)F5\224\250\135Y\1865/\30\191\171\140Q\213\182\133\145\224\148\190L\210{\143D, count: 228) =
     9.510 ( 0.014 ms): dirname/2805386 write(fd: 1, buf: /root/.tmux/plugins/tmux-continu, count: 43)        = 43 (kauditd)
     9.788 ( 0.007 ms): bash/2805385 write(fd: 1, buf: /root/.tmux/plugins/tmux-continu, count: 43)        = 43 (kauditd)
    13.865 ( 0.020 ms): :2805390/2805390 write(fd: 1, buf: 1.9\10, count: 4)                                   = 4 (kworker/R-rcu_g)
    15.183 ( 0.015 ms): tr/2805391 write(fd: 1, buf: 19, count: 2)                                       = 2 (kthreadd)
    15.715 ( 0.009 ms): bash/2805388 write(fd: 1, buf: 19\10, count: 3)                                    = 3 (pool_workqueue_)
    18.755 ( 0.014 ms): tmux/2805393 write(fd: 1, buf: tmux 3.4\10, count: 9)                              = 9 (kworker/0:0H-ev)
    19.737 ( 0.044 ms): sshd/2725386 write(fd: 4, buf: \188\197;\82d.1k\197\30\165[L@\153\139\192\173\247k\179kT.m\150\223\216\31\251\255, count: 316) =
    20.173 ( 0.008 ms): bash/2805396 write(fd: 1, buf: tmux 3.4\10, count: 9)                              = 9 (kworker/0:0H-ev)

Signed-off-by: Howard Chu <howardchu95@...il.com>
---
 tools/perf/builtin-trace.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 748b061f8678..74a5a3b9183a 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -4326,6 +4326,9 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 					sizeof(__u32), BPF_ANY);
 		}
 	}
+
+	/* For setting pids filter */
+	trace->filter_pids.map = trace->skel->maps.pids_filtered;
 #endif
 	err = trace__set_filter_pids(trace);
 	if (err < 0)
-- 
2.43.0