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[PATCH] Module per-cpu alignment cannot always be met
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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: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Rusty Russell authored and Linus Torvalds committed Aug 2, 2005
1 parent 561fb76 commit 842bbaa
Showing 1 changed file with 11 additions and 4 deletions.
15 changes: 11 additions & 4 deletions kernel/module.c
Original file line number Diff line number Diff line change
@@ -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;

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