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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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23
kernel/trace/ftrace.c
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@@ -326,6 +326,8 @@ int __register_ftrace_function(struct ftrace_ops *ops)
if (ops->flags & FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED)
ops->flags |= FTRACE_OPS_FL_SAVE_REGS;
#endif
if (!ftrace_enabled && (ops->flags & FTRACE_OPS_FL_PERMANENT))
return -EBUSY;
if (!core_kernel_data((unsigned long)ops))
ops->flags |= FTRACE_OPS_FL_DYNAMIC;
@@ -6754,6 +6756,18 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
}
EXPORT_SYMBOL_GPL(unregister_ftrace_function);
static bool is_permanent_ops_registered(void)
{
struct ftrace_ops *op;
do_for_each_ftrace_op(op, ftrace_ops_list) {
if (op->flags & FTRACE_OPS_FL_PERMANENT)
return true;
} while_for_each_ftrace_op(op);
return false;
}
int
ftrace_enable_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
@@ -6771,8 +6785,6 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
goto out;
last_ftrace_enabled = !!ftrace_enabled;
if (ftrace_enabled) {
/* we are starting ftrace again */
@@ -6783,12 +6795,19 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
ftrace_startup_sysctl();
} else {
if (is_permanent_ops_registered()) {
ftrace_enabled = true;
ret = -EBUSY;
goto out;
}
/* stopping ftrace calls (just send to ftrace_stub) */
ftrace_trace_function = ftrace_stub;
ftrace_shutdown_sysctl();
}
last_ftrace_enabled = !!ftrace_enabled;
out:
mutex_unlock(&ftrace_lock);
return ret;