On Tue, 1 Apr 2014 11:19:05 -0400 Prarit Bhargava <prarit@xxxxxxxxxx> wrote:
> When a module is built into the kernel the module_init() function becomes
> an initcall. Sometimes debugging through dynamic debug can help,
> however, debugging built in kernel modules is typically done by changing
> the .config, recompiling, and booting the new kernel in an effort to
> determine exactly which module caused a problem.
>
> This patchset can be useful stand-alone or combined with initcall_debug.
> There are cases where some initcalls can hang the machine before the
> console can be flushed, which can make initcall_debug output
> inaccurate. Having the ability to skip initcalls can help further
> debugging of these scenarios.
>
> Usage: initcall_blacklist=<list of comma separated initcalls>
>
> ex) added "initcall_blacklist=sgi_uv_sysfs_init" as a kernel parameter and
> the log contains:
>
> blacklisted initcall sgi_uv_sysfs_init
> ...
> ...
> function sgi_uv_sysfs_init returning without executing
>
> ex) added "initcall_blacklist=foo_bar,sgi_uv_sysfs_init" as a kernel parameter
> and the log contains:
>
> initcall blacklisted foo_bar
> initcall blacklisted sgi_uv_sysfs_init
> ...
> ...
> function sgi_uv_sysfs_init returning without executing
I guess the idea is reasonable and can be implemented very cheaply.
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1275,6 +1275,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> for working out where the kernel is dying during
> startup.
>
> + initcall_blacklist= [KNL] Do not execute a comma-separated list of
> + initcall functions. Useful for debugging built-in
> + modules and initcalls.
> initrd= [BOOT] Specify the location of the initial ramdisk
>
> inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
> diff --git a/init/main.c b/init/main.c
> index 9c7fd4c..e050c24 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -77,6 +77,7 @@
> #include <linux/sched_clock.h>
> #include <linux/context_tracking.h>
> #include <linux/random.h>
> +#include <linux/list.h>
>
> #include <asm/io.h>
> #include <asm/bugs.h>
> @@ -666,6 +667,42 @@ static void __init do_ctors(void)
> bool initcall_debug;
> core_param(initcall_debug, initcall_debug, bool, 0644);
>
> +struct blacklist_entry {
> + struct list_head next;
> + char *buf;
> +};
> +
> +static __initdata_or_module LIST_HEAD(blacklisted_initcalls);
I suggest this be moved inside #ifdef CONFIG_KALLSYMS, then add
#ifdef CONFIG_KALLSYMS
static bool initcall_blacklisted(const char *id)
{
...
}
#else
static bool initcall_blacklisted(const char *id)
{
return false;
}
#endif
than call that from do_one_initcall().
> +#ifdef CONFIG_KALLSYMS
> +static int __init initcall_blacklist(char *str)
> +{
> + char *str_entry;
> + struct blacklist_entry *entry;
> +
> + /* str argument is a comma-separated list of functions */
> + do {
> + str_entry = strsep(&str, ",");
> + if (str_entry) {
> + pr_debug("initcall blacklisted %s \n", str_entry);
> + entry = alloc_bootmem(sizeof(*entry));
> + entry->buf = alloc_bootmem(strlen(str_entry));
This needs to be strlen()+1.
> + strncpy(entry->buf, str_entry, strlen(str_entry));
and strcpy().
Or add a new strdup_bootmem() if it looks like there are (or will be)
other callers.
> + list_add(&entry->next, &blacklisted_initcalls);
> + }
> + } while (str_entry);
> +
> + return 0;
> +}
> +#else
> +static int __init initcall_blacklist(char *str)
> +{
> + pr_warning("initcall_blacklist requires CONFIG_KALLSYMS to be enabled.\n");
"initcall_blacklist requires CONFIG_KALLSYMS" is sufficient.
> + return 0;
> +}
> +#endif
> +__setup("initcall_blacklist=", initcall_blacklist);
> +
> static int __init_or_module do_one_initcall_debug(initcall_t fn)
> {
> ktime_t calltime, delta, rettime;
> @@ -689,6 +726,19 @@ int __init_or_module do_one_initcall(initcall_t fn)
> int count = preempt_count();
> int ret;
> char msgbuf[64];
> + char fn_name[128] = "\0";
> + struct list_head *tmp;
> + struct blacklist_entry *entry;
> +
> + snprintf(fn_name, 128, "%pf", fn);
Remove fn_name[], use kasprintf(), remember to free it.
> + list_for_each(tmp, &blacklisted_initcalls) {
> + entry = list_entry(tmp, struct blacklist_entry, next);
> + if (!strcmp(fn_name, entry->buf)) {
> + pr_debug("initcall %pf returning without executing\n",
"foo returning without executing" is contradictory: how can it return
if it didn't execute? I suggest something like "skipping blacklisted
initcall %pf".
> + fn);
> + return -EPERM;
> + }
> + }
Let's not leak all those blacklist entries when we're finished?
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