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SubjectWARNING at __ftrace_hash_rec_update()
On v3.1-7810-g094803e (current linus git), I'm able to trigger the below
FTRACE_WARN_ON() by running the following sequence of commands.
DYNAMIC_FTRACE is enabled.

ftrace.c:1384:
if (FTRACE_WARN_ON((rec->flags & ~FTRACE_FL_MASK) == 0))
return;
rec->flags--;

$ mount -t debugfs nodev /debug
$ cd /debug/tracing/
$ echo 0 > tracing_on
$ echo function > current_tracer
$ echo > set_ftrace_filter
$ echo 1 > tracing_on
$ cat trace
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
$ echo > set_ftrace_filter
[ 52.066435] ------------[ cut here ]------------
[ 52.066824] WARNING: at /home/rabin/kernel/kernel/trace/ftrace.c:1384 __ftrace_hash_rec_update.part.27+0x157/0x1a7()
[ 52.067794] Modules linked in:
[ 52.068260] Pid: 445, comm: bash Not tainted 3.1.0-07810-g094803e #29
[ 52.068702] Call Trace:
[ 52.068884] [<ffffffff8106fb26>] ? __ftrace_hash_rec_update.part.27+0x157/0x1a7
[ 52.069599] [<ffffffff81032347>] warn_slowpath_common+0x83/0x9b
[ 52.070122] [<ffffffff810758d9>] ? trace_parser_put+0xd/0xf
[ 52.070812] [<ffffffff81032379>] warn_slowpath_null+0x1a/0x1c
[ 52.071515] [<ffffffff8106fb26>] __ftrace_hash_rec_update.part.27+0x157/0x1a7
[ 52.072385] [<ffffffff8106fce2>] ftrace_hash_move+0x2e/0x151
[ 52.073075] [<ffffffff810bd028>] ? virt_to_head_page+0xe/0x31
[ 52.073748] [<ffffffff810befd7>] ? kfree+0x5e/0xd7
[ 52.074349] [<ffffffff8106feb8>] ftrace_regex_release+0xb3/0x107
[ 52.075098] [<ffffffff810c5085>] fput+0x8b/0x132
[ 52.075649] [<ffffffff810c24cf>] filp_close+0x63/0x6f
[ 52.076301] [<ffffffff810d043e>] sys_dup3+0x130/0x158
[ 52.076898] [<ffffffff810d04c4>] sys_dup2+0x5e/0x65
[ 52.077440] [<ffffffff81298db3>] ia32_do_call+0x13/0x13
[ 52.078097] ---[ end trace c723c025d087b7e9 ]---
$ cat trace
# tracer: function
#
# WARNING: FUNCTION TRACING IS CORRUPTED
# MAY BE MISSING FUNCTION EVENTS
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |



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