Re: FAILED: patch "[PATCH] module: weaken locking assertion for oops path." failed to apply to 4.1-stable tree

[Rusty Russell <rusty@rustcorp.com.au>]

gregkh@linuxfoundation.org writes:
> The patch below does not apply to the 4.1-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Hi Greg,

        That's OK.  But a question: this was implied by the Fixes: tag;
is there a better way to say "you need this IFF you have that"?

Thanks,
Rusty.

> ------------------ original commit in Linus's tree ------------------
>
>>>From fe0d34d242fa1e0dec059e774d146a705420bc9a Mon Sep 17 00:00:00 2001
> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Wed, 29 Jul 2015 05:52:14 +0930
> Subject: [PATCH] module: weaken locking assertion for oops path.
>
> We don't actually hold the module_mutex when calling find_module_all
> from module_kallsyms_lookup_name: that's because it's used by the oops
> code and we don't want to deadlock.
>
> However, access to the list read-only is safe if preempt is disabled,
> so we can weaken the assertion.  Keep a strong version for external
> callers though.
>
> Fixes: 0be964be0d45 ("module: Sanitize RCU usage and locking")
> Reported-by: He Kuang <hekuang@huawei.com>
> Cc: stable@kernel.org
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 4d2b82e610e2..b86b7bf1be38 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -602,13 +602,16 @@ const struct kernel_symbol *find_symbol(const char *name,
>  }
>  EXPORT_SYMBOL_GPL(find_symbol);
>  
> -/* Search for module by name: must hold module_mutex. */
> +/*
> + * Search for module by name: must hold module_mutex (or preempt disabled
> + * for read-only access).
> + */
>  static struct module *find_module_all(const char *name, size_t len,
>  				      bool even_unformed)
>  {
>  	struct module *mod;
>  
> -	module_assert_mutex();
> +	module_assert_mutex_or_preempt();
>  
>  	list_for_each_entry(mod, &modules, list) {
>  		if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
> @@ -621,6 +624,7 @@ static struct module *find_module_all(const char *name, size_t len,
>  
>  struct module *find_module(const char *name)
>  {
> +	module_assert_mutex();
>  	return find_module_all(name, strlen(name), false);
>  }
>  EXPORT_SYMBOL_GPL(find_module);