[PATCH 6/6] kmod: make __request_module() killable

From: Oleg Nesterov
Date: Tue Feb 14 2012 - 11:56:06 EST


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

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
kernel/kmod.c | 26 ++++++++++++++++++++++++--
1 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 56a29e8..957a7aa 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -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;
}

/**
--
1.5.5.1


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/