Commit 1cc684ab authored Mar 23, 2012 by Oleg Nesterov Committed by Linus Torvalds Mar 23, 2012

kmod: make __request_module() killable



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>

parent 3e63a93b

kernel/kmod.c

+24 −2

Original line number	Diff line number	Diff line
		@@ -60,6 +60,12 @@ static DECLARE_RWSEM(umhelper_sem);
		*/
		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[] = {
		@@ -69,10 +75,26 @@ 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;
		}

		/**

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