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Subject[ 014/184] kmod: make __request_module() killable
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@redhat.com>

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>
[dannf, bwh: backported to Debian's 2.6.32]
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
kernel/kmod.c | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 1088a8f..8ecc509 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -53,16 +53,48 @@ static DECLARE_RWSEM(umhelper_sem);
*/
char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";

+static void free_modprobe_argv(char **argv, char **envp)
+{
+ kfree(argv[3]); /* check call_modprobe() */
+ kfree(argv);
+}
+
static int call_modprobe(char *module_name, int wait)
{
static char *envp[] = { "HOME=/",
"TERM=linux",
"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
NULL };
+ struct subprocess_info *info;
+
+ char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
+ if (!argv)
+ goto out;

- char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
+ module_name = kstrdup(module_name, GFP_KERNEL);
+ if (!module_name)
+ goto free_argv;

- return call_usermodehelper(modprobe_path, argv, envp, wait);
+ argv[0] = modprobe_path;
+ argv[1] = "-q";
+ argv[2] = "--";
+ argv[3] = module_name; /* check free_modprobe_argv() */
+ argv[4] = NULL;
+
+ info = call_usermodehelper_setup(argv[0], argv, envp, GFP_ATOMIC);
+ if (!info)
+ goto free_module_name;
+
+ call_usermodehelper_setcleanup(info, free_modprobe_argv);
+
+ return call_usermodehelper_exec(info, wait | UMH_KILLABLE);
+
+free_module_name:
+ kfree(module_name);
+free_argv:
+ kfree(argv);
+out:
+ return -ENOMEM;
}

/**
--
1.7.12.2.21.g234cd45.dirty




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