powerpc/perf_counter: Fix vdso detection

perf_counter uses arch_vma_name() to detect a vdso region which in turn uses
current->mm->context.vdso_base. We need to initialise this before doing
the mmap or else we fail to detect the vdso.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 3faaf29bdb29def5748cf54beef11a285764e438..94e2df3cae074d2fe5ca514f21960d57b9b3c9a3 100644 (file)
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -240,6 +240,13 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
                goto fail_mmapsem;
        }
 
+       /*
+        * Put vDSO base into mm struct. We need to do this before calling
+        * install_special_mapping or the perf counter mmap tracking code
+        * will fail to recognise it as a vDSO (since arch_vma_name fails).
+        */
+       current->mm->context.vdso_base = vdso_base;
+
        /*
         * our vma flags don't have VM_WRITE so by default, the process isn't
         * allowed to write those pages.
@@ -260,11 +267,10 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
                                     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
                                     VM_ALWAYSDUMP,
                                     vdso_pagelist);
-       if (rc)
+       if (rc) {
+               current->mm->context.vdso_base = 0;
                goto fail_mmapsem;
-
-       /* Put vDSO base into mm struct */
-       current->mm->context.vdso_base = vdso_base;
+       }
 
        up_write(&mm->mmap_sem);
        return 0;