x86: mm: move mmap_sem unlock from mm_fault_error() to caller

commit 7fb08eca upstream.

This replaces four copies in various stages of mm_fault_error() handling
with just a single one.  It will also allow for more natural placement
of the unlocking after some further cleanup.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

arch/x86/mm/fault.c

@@ -833,11 +833,8 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 	  unsigned int fault)
 {
 	struct task_struct *tsk = current;
-	struct mm_struct *mm = tsk->mm;
 	int code = BUS_ADRERR;
 
-	up_read(&mm->mmap_sem);
-
 	/* Kernel mode? Handle exceptions or die: */
 	if (!(error_code & PF_USER)) {
 		no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
@@ -868,7 +865,6 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 	       unsigned long address, unsigned int fault)
 {
 	if (fatal_signal_pending(current) && !(error_code & PF_USER)) {
-		up_read(&current->mm->mmap_sem);
 		no_context(regs, error_code, address, 0, 0);
 		return;
 	}
@@ -876,14 +872,11 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 	if (fault & VM_FAULT_OOM) {
 		/* Kernel mode? Handle exceptions or die: */
 		if (!(error_code & PF_USER)) {
-			up_read(&current->mm->mmap_sem);
 			no_context(regs, error_code, address,
 				   SIGSEGV, SEGV_MAPERR);
 			return;
 		}
 
-		up_read(&current->mm->mmap_sem);
-
 		/*
 		 * We ran out of memory, call the OOM killer, and return the
 		 * userspace (which will retry the fault, or kill us if we got
@@ -1215,6 +1208,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
+		up_read(&mm->mmap_sem);
 		mm_fault_error(regs, error_code, address, fault);
 		return;
 	}