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ftrace: Introduce PERMANENT ftrace_ops flag

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Livepatch uses ftrace for redirection to new patched functions. It means
that if ftrace is disabled, all live patched functions are disabled as
well. Toggling global 'ftrace_enabled' sysctl thus affect it directly.
It is not a problem per se, because only administrator can set sysctl
values, but it still may be surprising.

Introduce PERMANENT ftrace_ops flag to amend this. If the
FTRACE_OPS_FL_PERMANENT is set on any ftrace ops, the tracing cannot be
disabled by disabling ftrace_enabled. Equally, a callback with the flag
set cannot be registered if ftrace_enabled is disabled.

Link: http://lkml.kernel.org/r/20191016113316.13415-2-mbenes@suse.cz

Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Miroslav Benes 2019-10-16 13:33:13 +02:00 • committed by Steven Rostedt
parent a99d8080aa
commit 7162431dcf
5 changed files with 37 additions and 4 deletions
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3
include/linux/ftrace.h
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@ -142,6 +142,8 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
* PID - Is affected by set_ftrace_pid (allows filtering on those pids)
* RCU - Set when the ops can only be called when RCU is watching.
* TRACE_ARRAY - The ops->private points to a trace_array descriptor.
* PERMANENT - Set when the ops is permanent and should not be affected by
* ftrace_enabled.
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
@ -160,6 +162,7 @@ enum {
FTRACE_OPS_FL_PID = 1 << 13,
FTRACE_OPS_FL_RCU = 1 << 14,
FTRACE_OPS_FL_TRACE_ARRAY = 1 << 15,
FTRACE_OPS_FL_PERMANENT = 1 << 16,
};
#ifdef CONFIG_DYNAMIC_FTRACE