module: create a request_module_nowait()

There seems to be a common pattern in the kernel where drivers want to
call request_module() from inside a module_init() function. Currently
this would deadlock.

As a result, several drivers go through hoops like scheduling things via
kevent, or creating custom work queues (because kevent can deadlock on them).

This patch changes this to use a request_module_nowait() function macro instead,
which just fires the modprobe off but doesn't wait for it, and thus avoids the
original deadlock entirely.

On my laptop this already results in one less kernel thread running..

(Includes Jiri's patch to use enum umh_wait)

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (bool-ified)
Cc: Jiri Slaby <jirislaby@gmail.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 92213a9194e1..d5fa565086d1 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -29,10 +29,15 @@
 #ifdef CONFIG_MODULES
 /* modprobe exit status on success, -ve on error.  Return value
  * usually useless though. */
-extern int request_module(const char * name, ...) __attribute__ ((format (printf, 1, 2)));
-#define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
+extern int __request_module(bool wait, const char *name, ...) \
+        __attribute__((format(printf, 2, 3)));
+#define request_module(mod...) __request_module(true, mod)
+#define request_module_nowait(mod...) __request_module(false, mod)
+#define try_then_request_module(x, mod...) \
+        ((x) ?: (__request_module(false, mod), (x)))
 #else
-static inline int request_module(const char * name, ...) { return -ENOSYS; }
+static inline int request_module(const char *name, ...) { return -ENOSYS; }
+static inline int request_module_nowait(const char *name, ...) { return -ENOSYS; }
 #define try_then_request_module(x, mod...) (x)
 #endif