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Commit 842bbaaa authored by Rusty Russell's avatar Rusty Russell Committed by Linus Torvalds
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[PATCH] Module per-cpu alignment cannot always be met 

The module code assumes noone will ever ask for a per-cpu area more than
SMP_CACHE_BYTES aligned.  However, as these cases show, gcc asks sometimes
asks for 32-byte alignment for the per-cpu section on a module, and if
CONFIG_X86_L1_CACHE_SHIFT is 4, we hit that BUG_ON().  This is obviously an
unusual combination, as there have been few reports, but better to warn
than die.

See:
	http://www.ussg.iu.edu/hypermail/linux/kernel/0409.0/0768.html

And more recently:
	http://bugs.gentoo.org/show_bug.cgi?id=97006



Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 561fb765

kernel/module.c

+11 −4
Original line number Diff line number Diff line
@@ -250,13 +250,18 @@ static inline unsigned int block_size(int val) 
/* Created by linker magic */

extern char __per_cpu_start[], __per_cpu_end[];



static void *percpu_modalloc(unsigned long size, unsigned long align)

static void *percpu_modalloc(unsigned long size, unsigned long align,

			     const char *name)

{

	unsigned long extra;

	unsigned int i;

	void *ptr;



	BUG_ON(align > SMP_CACHE_BYTES);

	if (align > SMP_CACHE_BYTES) {

		printk(KERN_WARNING "%s: per-cpu alignment %li > %i\n",

		       name, align, SMP_CACHE_BYTES);

		align = SMP_CACHE_BYTES;

	}



	ptr = __per_cpu_start;

	for (i = 0; i < pcpu_num_used; ptr += block_size(pcpu_size[i]), i++) {
@@ -348,7 +353,8 @@ static int percpu_modinit(void) 
}	

__initcall(percpu_modinit);

#else /* ... !CONFIG_SMP */

static inline void *percpu_modalloc(unsigned long size, unsigned long align)

static inline void *percpu_modalloc(unsigned long size, unsigned long align,

				    const char *name)

{

	return NULL;

}
@@ -1644,7 +1650,8 @@ static struct module *load_module(void __user *umod, 
	if (pcpuindex) {

		/* We have a special allocation for this section. */

		percpu = percpu_modalloc(sechdrs[pcpuindex].sh_size,

					 sechdrs[pcpuindex].sh_addralign);

					 sechdrs[pcpuindex].sh_addralign,

					 mod->name);

		if (!percpu) {

			err = -ENOMEM;

			goto free_mod;