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| author | Tejun Heo <tj@kernel.org> | 2013-01-22 16:48:03 -0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2013-01-22 16:48:03 -0800 |
| commit | 0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4 (patch) | |
| tree | 361b0d7f16f03c4e9f196882df5245faa4ac7138 /kernel/kmod.c | |
| parent | 21c3c5d2800733b7a276725b8e1ae49a694adc1a (diff) | |
| download | lwn-0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4.tar.gz lwn-0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4.zip | |
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>
Diffstat (limited to 'kernel/kmod.c')
| -rw-r--r-- | kernel/kmod.c | 9 |
1 files changed, 9 insertions, 0 deletions
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 <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); |