ARM: fix a cockup in 48be69a02 (ARM: move signal handlers into a vdso-like page)

Unfortunately, I never committed the fix to a nasty oops which can
occur as a result of that commit:

------------[ cut here ]------------
kernel BUG at /home/olof/work/batch/include/linux/mm.h:414!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 490 Comm: killall5 Not tainted 3.11.0-rc3-00288-gabe0308 #53
task: e90acac0 ti: e9be8000 task.ti: e9be8000
PC is at special_mapping_fault+0xa4/0xc4
LR is at __do_fault+0x68/0x48c

This doesn't show up unless you do quite a bit of testing; a simple
boot test does not do this, so all my nightly tests were passing fine.

The reason for this is that install_special_mapping() expects the
page array to stick around, and as this was only inserting one page
which was stored on the kernel stack, that's why this was blowing up.

Reported-by: Olof Johansson <olof@lixom.net>
Tested-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 19 insertions, 22 deletions

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 0f17e06..39e7105 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -614,35 +614,32 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 	return 0;
 }
 
-static struct page *signal_page;
-
 struct page *get_signal_page(void)
 {
-	if (!signal_page) {
-		unsigned long ptr;
-		unsigned offset;
-		void *addr;
+	unsigned long ptr;
+	unsigned offset;
+	struct page *page;
+	void *addr;
 
-		signal_page = alloc_pages(GFP_KERNEL, 0);
+	page = alloc_pages(GFP_KERNEL, 0);
 
-		if (!signal_page)
-			return NULL;
+	if (!page)
+		return NULL;
 
-		addr = page_address(signal_page);
+	addr = page_address(page);
 
-		/* Give the signal return code some randomness */
-		offset = 0x200 + (get_random_int() & 0x7fc);
-		signal_return_offset = offset;
+	/* Give the signal return code some randomness */
+	offset = 0x200 + (get_random_int() & 0x7fc);
+	signal_return_offset = offset;
 
-		/*
-		 * Copy signal return handlers into the vector page, and
-		 * set sigreturn to be a pointer to these.
-		 */
-		memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
+	/*
+	 * Copy signal return handlers into the vector page, and
+	 * set sigreturn to be a pointer to these.
+	 */
+	memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
 
-		ptr = (unsigned long)addr + offset;
-		flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
-	}
+	ptr = (unsigned long)addr + offset;
+	flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
 
-	return signal_page;
+	return page;
 }