kmod: make __request_module() killable

commit 1cc684ab75123efe7ff446eb821d44375ba8fa30 upstream.

As Tetsuo Handa pointed out, request_module() can stress the system
while the oom-killed caller sleeps in TASK_UNINTERRUPTIBLE.

The task T uses "almost all" memory, then it does something which
triggers request_module().  Say, it can simply call sys_socket().  This
in turn needs more memory and leads to OOM.  oom-killer correctly
chooses T and kills it, but this can't help because it sleeps in
TASK_UNINTERRUPTIBLE and after that oom-killer becomes "disabled" by the
TIF_MEMDIE task T.

Make __request_module() killable.  The only necessary change is that
call_modprobe() should kmalloc argv and module_name, they can't live in
the stack if we use UMH_KILLABLE.  This memory is freed via
call_usermodehelper_freeinfo()->cleanup.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 135041f..d6fe08a 100644 (file)
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -58,6 +58,12 @@ static DEFINE_SPINLOCK(umh_sysctl_lock);
 */
 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
 
+static void free_modprobe_argv(struct subprocess_info *info)
+{
+       kfree(info->argv[3]); /* check call_modprobe() */
+       kfree(info->argv);
+}
+
 static int call_modprobe(char *module_name, int wait)
 {
        static char *envp[] = {
@@ -67,10 +73,26 @@ static int call_modprobe(char *module_name, int wait)
                NULL
        };
 
-       char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
+       char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
+       if (!argv)
+               goto out;
+
+       module_name = kstrdup(module_name, GFP_KERNEL);
+       if (!module_name)
+               goto free_argv;
+
+       argv[0] = modprobe_path;
+       argv[1] = "-q";
+       argv[2] = "--";
+       argv[3] = module_name;  /* check free_modprobe_argv() */
+       argv[4] = NULL;
 
        return call_usermodehelper_fns(modprobe_path, argv, envp,
-                                       wait, NULL, NULL, NULL);
+               wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
+free_argv:
+       kfree(argv);
+out:
+       return -ENOMEM;
 }
 
 /**