From: "Steven Rostedt (Red Hat)" In the loop of ftrace_save_ops_tramp_hash(), it adds all the recs to the ops hash if the rec has only one callback attached and the ops is connected to the rec. It gives a nasty warning and shuts down ftrace if the rec doesn't have a trampoline set for it. But this can happen with the following scenario: # cd /sys/kernel/debug/tracing # echo schedule do_IRQ > set_ftrace_filter # mkdir instances/foo # echo schedule > instances/foo/set_ftrace_filter # echo function_graph > current_function # echo function > instances/foo/current_function # echo nop > instances/foo/current_function The above would then trigger the following warning and disable ftrace: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 3145 at kernel/trace/ftrace.c:2212 ftrace_run_update_code+0xe4/0x15b() Modules linked in: ipt_MASQUERADE sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ip [...] CPU: 1 PID: 3145 Comm: bash Not tainted 3.16.0-rc3-test+ #136 Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007 0000000000000000 ffffffff81808a88 ffffffff81502130 0000000000000000 ffffffff81040ca1 ffff880077c08000 ffffffff810bd286 0000000000000001 ffffffff81a56830 ffff88007a041be0 ffff88007a872d60 00000000000001be Call Trace: [] ? dump_stack+0x4a/0x75 [] ? warn_slowpath_common+0x7e/0x97 [] ? ftrace_run_update_code+0xe4/0x15b [] ? ftrace_run_update_code+0xe4/0x15b [] ? ftrace_shutdown+0x11c/0x16b [] ? unregister_ftrace_function+0x1e/0x38 [] ? function_trace_reset+0x1a/0x28 [] ? tracing_set_tracer+0xc1/0x276 [] ? tracing_set_trace_write+0x73/0x91 [] ? __sb_start_write+0x9a/0xcc [] ? security_file_permission+0x1b/0x31 [] ? vfs_write+0xac/0x11c [] ? SyS_write+0x60/0x8e [] ? system_call_fastpath+0x16/0x1b ---[ end trace 938c4415cbc7dc96 ]--- ------------[ cut here ]------------ Link: http://lkml.kernel.org/r/20140723120805.GB21376@redhat.com Reported-by: Oleg Nesterov Signed-off-by: Steven Rostedt --- kernel/trace/ftrace.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index eda69c9f78d0..6ef1989c2b2e 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2208,6 +2208,14 @@ static int ftrace_save_ops_tramp_hash(struct ftrace_ops *ops) if (ftrace_rec_count(rec) == 1 && ftrace_ops_test(ops, rec->ip, rec)) { + /* + * If another ops adds to a rec, the rec will + * lose its trampoline and never get it back + * until all ops are off of it. + */ + if (!(rec->flags & FTRACE_FL_TRAMP)) + continue; + /* This record had better have a trampoline */ if (FTRACE_WARN_ON(!(rec->flags & FTRACE_FL_TRAMP_EN))) return -1; -- 2.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/