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authorOleg Nesterov <oleg@redhat.com>2012-03-23 15:02:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-23 16:58:41 -0700
commitd0bd587a80960d7ba7e0c8396e154028c9045c54 (patch)
tree3765f8eccdc5f982ba173a7a05d8981d573b9486
parentb3449922502f5a161ee2b5022a33aec8472fbf18 (diff)
usermodehelper: implement UMH_KILLABLE
Implement UMH_KILLABLE, should be used along with UMH_WAIT_EXEC/PROC. The caller must ensure that subprocess_info->path/etc can not go away until call_usermodehelper_freeinfo(). call_usermodehelper_exec(UMH_KILLABLE) does wait_for_completion_killable. If it fails, it uses xchg(&sub_info->complete, NULL) to serialize with umh_complete() which does the same xhcg() to access sub_info->complete. If call_usermodehelper_exec wins, it can safely return. umh_complete() should get NULL and call call_usermodehelper_freeinfo(). Otherwise we know that umh_complete() was already called, in this case call_usermodehelper_exec() falls back to wait_for_completion() which should succeed "very soon". Note: UMH_NO_WAIT == -1 but it obviously should not be used with UMH_KILLABLE. We delay the neccessary cleanup to simplify the back porting. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> 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>
-rw-r--r--include/linux/kmod.h2
-rw-r--r--kernel/kmod.c27
2 files changed, 27 insertions, 2 deletions
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 722f477c4ef7..1b5985855ffc 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -54,6 +54,8 @@ enum umh_wait {
UMH_WAIT_PROC = 1, /* wait for the process to complete */
};
+#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
+
struct subprocess_info {
struct work_struct work;
struct completion *complete;
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 8ea25944ce33..f92f917c450c 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -201,7 +201,15 @@ EXPORT_SYMBOL(call_usermodehelper_freeinfo);
static void umh_complete(struct subprocess_info *sub_info)
{
- complete(sub_info->complete);
+ struct completion *comp = xchg(&sub_info->complete, NULL);
+ /*
+ * See call_usermodehelper_exec(). If xchg() returns NULL
+ * we own sub_info, the UMH_KILLABLE caller has gone away.
+ */
+ if (comp)
+ complete(comp);
+ else
+ call_usermodehelper_freeinfo(sub_info);
}
/* Keventd can't block, but this (a child) can. */
@@ -252,6 +260,9 @@ static void __call_usermodehelper(struct work_struct *work)
enum umh_wait wait = sub_info->wait;
pid_t pid;
+ if (wait != UMH_NO_WAIT)
+ wait &= ~UMH_KILLABLE;
+
/* CLONE_VFORK: wait until the usermode helper has execve'd
* successfully We need the data structures to stay around
* until that is done. */
@@ -461,9 +472,21 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
queue_work(khelper_wq, &sub_info->work);
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
goto unlock;
+
+ if (wait & UMH_KILLABLE) {
+ retval = wait_for_completion_killable(&done);
+ if (!retval)
+ goto wait_done;
+
+ /* umh_complete() will see NULL and free sub_info */
+ if (xchg(&sub_info->complete, NULL))
+ goto unlock;
+ /* fallthrough, umh_complete() was already called */
+ }
+
wait_for_completion(&done);
+wait_done:
retval = sub_info->retval;
-
out:
call_usermodehelper_freeinfo(sub_info);
unlock: