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>

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 3faaf29..94e2df3 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -241,6 +241,13 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	}
 
 	/*
+	 * 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.
 	 * gdb can break that with ptrace interface, and thus trigger COW on
@@ -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;