From 0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 22 Jan 2013 16:48:03 -0800 Subject: [PATCH] async, kmod: warn on synchronous request_module() from async workers 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 Reported-by: Alex Riesen Cc: Linus Torvalds Cc: Arjan van de Ven --- kernel/kmod.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/kmod.c b/kernel/kmod.c index 1c317e386831..ecd42b484db8 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -38,6 +38,7 @@ #include #include #include +#include #include #include @@ -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);