On 2022/9/20 20:08, Petr Mladek wrote:

On Fri 2022-09-09 21:00:15, Zhen Lei wrote:

quoted

Currently we traverse all symbols of all modules to find the specified
function for the specified module. But in reality, we just need to find
the given module and then traverse all the symbols in it.

I agree that it might be noticeable speedup.

quoted

In order to achieve this purpose, split the call to hook 'fn' into two
phases:
1. Finds the given module. Pass pointer 'mod'. Hook 'fn' directly returns
   the comparison result of the module name without comparing the function
   name.
2. Finds the given function in that module. Pass pointer 'mod = NULL'.
   Hook 'fn' skip the comparison of module name and directly compare
   function names.

Phase1: mod1-->mod2..(subsequent modules do not need to be compared)
                |
Phase2:          -->f1-->f2-->f3

Signed-off-by: Zhen Lei <redacted>
---
 kernel/livepatch/core.c  |  7 ++-----
 kernel/module/kallsyms.c | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 31b57ccf908017e..98e23137e4133bc 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c

@@ -130,15 +130,12 @@ static int klp_find_callback(void *data, const char *name,
 {
 	struct klp_find_arg *args = data;
 
-	if ((mod && !args->objname) || (!mod && args->objname))
-		return 0;
+	if (mod)
+		return strcmp(args->objname, mod->name);
 
 	if (strcmp(args->name, name))
 		return 0;
 
-	if (args->objname && strcmp(args->objname, mod->name))
-		return 0;
-
 	args->addr = addr;
 	args->count++;
 

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index f5c5c9175333df7..b033613e6c7e3bb 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c

@@ -510,6 +510,11 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
 		if (mod->state == MODULE_STATE_UNFORMED)
 			continue;
 
+		/* check mod->name first */
+		ret = fn(data, NULL, mod, 0);
+		if (ret)
+			continue;

Hmm, it somehow gets too complicated. The same fn() callback has to
behave correctly in 3 different situations. I would suggest to
simplify everything:


1. Pass the requested modname as a parameter to module_kallsyms_on_each_symbol()

/*
 * Iterate over all symbols in the given @modname. For symbols from
 * vmlinux use kallsyms_on_each_symbol() instead.
 */
int module_kallsyms_on_each_symbol(const char *modname,
				   int (*fn)(void *, const char *,
					     struct module *, unsigned long),
				   void *data)

and do here:

		if (strcmp(modname, mod->name))
			continue;

Right, looks good. This makes the code logic much clearer. Thanks.

2. We do not even need to pass .objname in struct klp_find_arg
   could simplify the callback:

Yes

static int klp_find_callback(void *data, const char *name,
			     struct module *mod, unsigned long addr)
{
	struct klp_find_arg *args = data;

	if (strcmp(args->name, name))
		return 0;

	args->addr = addr;
	args->count++;

	/*
	 * Finish the search when the symbol is found for the desired position
	 * or the position is not defined for a non-unique symbol.
	 */
	if ((args->pos && (args->count == args->pos)) ||
	    (!args->pos && (args->count > 1)))
		return 1;

	return 0;
}

3. As a result the *mod parameter won't be used by any existing
   fn() callback and could be removed. This should be done as
   a separate patch. It touches also ftrace_lookup_symbols().

OK, I will do it tomorrow. The next version is v5.

Best Regards,
Petr
.

-- 
Regards,
  Zhen Lei