Messages in this thread Patch in this message | | | Date | Wed, 05 Apr 2017 12:21:13 -0400 | From | Steven Rostedt <> | Subject | [for-next][PATCH 4/7] ftrace: Update func_pos in t_start() when all functions are enabled |
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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
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) <rostedt@goodmis.org> --- 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; -- 2.10.2
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