sg: disable interrupts inside sg_copy_buffer

The callers of sg_copy_buffer must disable interrupts before calling
it (since it uses kmap_atomic). Some callers use it on
interrupt-disabled code but some need to take the trouble to disable
interrupts just for this. No wonder they forget about it and we hit a
bug like:

http://bugzilla.kernel.org/show_bug.cgi?id=11529

James said that it might be better to disable interrupts inside the
function rather than risk the callers getting it wrong.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

lib/scatterlist.c

@@ -422,9 +422,12 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 {
 	unsigned int offset = 0;
 	struct sg_mapping_iter miter;
+	unsigned long flags;
 
 	sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
 
+	local_irq_save(flags);
+
 	while (sg_miter_next(&miter) && offset < buflen) {
 		unsigned int len;
 
@@ -442,6 +445,7 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 
 	sg_miter_stop(&miter);
 
+	local_irq_restore(flags);
 	return offset;
 }