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authorRusty Russell <rusty@rustcorp.com.au>2009-03-31 13:05:35 -0600
committerRusty Russell <rusty@rustcorp.com.au>2009-03-31 13:05:35 +1030
commite91defa26c527ceeaff6266c55cdc7e17c9081a2 (patch)
tree03554f76949e5b1bcd4e640a10846d9540b97640
parentacae05156551fd7528fbb616271e672789388e3c (diff)
module: don't use stop_machine on module load
Kay Sievers <kay.sievers@vrfy.org> discovered that boot times are slowed by about half a second because all the stop_machine_create() calls, and he only probes about 40 modules (I have 125 loaded on this laptop). We only do stop_machine_create() so we can unlink the module if something goes wrong, but it's overkill (and buggy anyway: if stop_machine_create() fails we still call stop_machine_destroy()). Since we are only protecting against kallsyms (esp. oops) walking the list, synchronize_sched() is sufficient (synchronize_rcu() is probably sufficient, but we're not in a hurry). Kay says of this patch: ... no module takes more than 40 millisecs to link now, most of them are between 3 and 8 millisecs. That looks very different to the numbers without this patch and the otherwise same setup, where we get heavy noise in the traces and many delays of up to 200 millisecs until linking, most of them taking 30+ millisecs. Tested-by: Kay Sievers <kay.sievers@vrfy.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--kernel/module.c12
1 files changed, 3 insertions, 9 deletions
diff --git a/kernel/module.c b/kernel/module.c
index e8cf636e614..1a9a3986b13 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1912,12 +1912,6 @@ static noinline struct module *load_module(void __user *umod,
if (len > 64 * 1024 * 1024 || (hdr = vmalloc(len)) == NULL)
return ERR_PTR(-ENOMEM);
- /* Create stop_machine threads since the error path relies on
- * a non-failing stop_machine call. */
- err = stop_machine_create();
- if (err)
- goto free_hdr;
-
if (copy_from_user(hdr, umod, len) != 0) {
err = -EFAULT;
goto free_hdr;
@@ -2303,12 +2297,13 @@ static noinline struct module *load_module(void __user *umod,
/* Get rid of temporary copy */
vfree(hdr);
- stop_machine_destroy();
/* Done! */
return mod;
unlink:
- stop_machine(__unlink_module, mod, NULL);
+ /* Unlink carefully: kallsyms could be walking list. */
+ list_del_rcu(&mod->list);
+ synchronize_sched();
module_arch_cleanup(mod);
cleanup:
kobject_del(&mod->mkobj.kobj);
@@ -2331,7 +2326,6 @@ static noinline struct module *load_module(void __user *umod,
kfree(args);
free_hdr:
vfree(hdr);
- stop_machine_destroy();
return ERR_PTR(err);
truncated: