>From 4983f3b51e18d008956dd113e0ea2f252774cefc Mon Sep 17 00:00:00 2001 From: Tejun Heo <t...@kernel.org> Date: Fri, 18 Jan 2013 14:05:57 -0800
Synchronous requet_module() from an async worker can lead to deadlock because module init path may invoke async_synchronize_full(). The async worker waits for request_module() to complete and the module loading waits for the async task to finish. This bug happened in the block layer because of default elevator auto-loading. Block layer has been updated not to do default elevator auto-loading and it has been decided to disallow synchronous request_module() from async workers. Trigger WARN_ON_ONCE() on synchronous request_module() from async workers. For more details, please refer to the following thread. http://thread.gmane.org/gmane.linux.kernel/1420814 Signed-off-by: Tejun Heo <t...@kernel.org> Reported-by: Alex Riesen <raa.l...@gmail.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Arjan van de Ven <ar...@linux.intel.com> --- kernel/kmod.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/kmod.c b/kernel/kmod.c index 1c317e3..ecd42b4 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -38,6 +38,7 @@ #include <linux/suspend.h> #include <linux/rwsem.h> #include <linux/ptrace.h> +#include <linux/async.h> #include <asm/uaccess.h> #include <trace/events/module.h> @@ -130,6 +131,14 @@ int __request_module(bool wait, const char *fmt, ...) #define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */ static int kmod_loop_msg; + /* + * We don't allow synchronous module loading from async. Module + * init may invoke async_synchronize_full() which will end up + * waiting for this task which already is waiting for the module + * loading to complete, leading to a deadlock. + */ + WARN_ON_ONCE(wait && current_is_async()); + va_start(args, fmt); ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args); va_end(args); -- 1.8.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
