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authorTejun Heo <tj@kernel.org>2013-01-22 16:48:03 -0800
committerTejun Heo <tj@kernel.org>2013-01-22 16:48:03 -0800
commit0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4 (patch)
tree361b0d7f16f03c4e9f196882df5245faa4ac7138
parent21c3c5d2800733b7a276725b8e1ae49a694adc1a (diff)
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 <tj@kernel.org> Reported-by: Alex Riesen <raa.lkml@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Arjan van de Ven <arjan@linux.intel.com>
-rw-r--r--kernel/kmod.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 1c317e38683..ecd42b484db 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);