linux-kernel - Re: [PATCH v2 6/9] s390/module: Use s390_kernel

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Date:   Wed, 22 Apr 2020 14:28:26 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>, linux-s390@...r.kernel.org,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late
 relocations

> +int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
> +		       unsigned int symindex, unsigned int relsec,
> +		       struct module *me)
> +{
> +	int ret;
> +	bool early = me->state == MODULE_STATE_UNFORMED;
> +	void *(*write)(void *, const void *, size_t) = memcpy;
> +
> +	if (!early) {
> +		write = s390_kernel_write;
> +		mutex_lock(&text_mutex);
> +	}
> +
> +	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
> +				   write);
> +
> +	if (!early)
> +		mutex_unlock(&text_mutex);
> +
> +	return ret;
> +}

It means that you can take text_mutex the second time here because it 
is still taken in klp_init_object_loaded(). It is removed later in the 
series though. The same applies for x86 patch.

Also, s390_kernel_write() grabs s390_kernel_write_lock spinlock before 
writing anything, so maybe text_mutex is not really needed as long as 
s390_kernel_write is called everywhere for text patching.

Miroslav