From 43ff926a0c3a0cfd6aa313c3232420f009ab43e8 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Thu, 30 Mar 2017 16:51:43 -0400 Subject: [PATCH] ftrace: Update func_pos in t_start() when all functions are enabled If all functions are enabled, there's a comment displayed in the file to denote that: # cd /sys/kernel/debug/tracing # cat set_ftrace_filter #### all functions enabled #### If a function trigger is set, those are displayed as well: # echo schedule:traceoff >> /debug/tracing/set_ftrace_filter # cat set_ftrace_filter #### all functions enabled #### schedule:traceoff:unlimited But if you read that file with dd, the output can change: # dd if=/debug/tracing/set_ftrace_filter bs=1 #### all functions enabled #### 32+0 records in 32+0 records out 32 bytes copied, 7.0237e-05 s, 456 kB/s This is because the "pos" variable is updated for the comment, but func_pos is not. "func_pos" is used by the triggers (or hashes) to know how many functions were printed and it bases its index from the pos - func_pos. func_pos should be 1 to count for the comment printed. But since it is not, t_hash_start() thinks that one trigger was already printed. The cat gets to t_hash_start() via t_next() and not t_start() which updates both pos and func_pos. Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ftrace.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 421530831ddd..d4b18ce9ba88 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3230,6 +3230,7 @@ static void *t_start(struct seq_file *m, loff_t *pos) */ if ((iter->flags & (FTRACE_ITER_FILTER | FTRACE_ITER_NOTRACE)) && ftrace_hash_empty(iter->hash)) { + iter->func_pos = 1; /* Account for the message */ if (*pos > 0) return t_hash_start(m, pos); iter->flags |= FTRACE_ITER_PRINTALL; -- 2.20.1