X-Git-Url: http://pilppa.org/gitweb/gitweb.cgi?a=blobdiff_plain;f=mm%2Fmadvise.c;h=93ee375b38e7edc7b414b7a2b6891411a45d0b0c;hb=c86da3a3d40f6e7a032edfaea191fb51e9626c8f;hp=603c5257ed6efecaadde1e4047ec60ff1f22dfaa;hpb=e676853c8c3f77166c03f1eea7dab6e854eeb819;p=linux-2.6-omap-h63xx.git

diff --git a/mm/madvise.c b/mm/madvise.c
index 603c5257ed6..93ee375b38e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -10,6 +10,25 @@
 #include <linux/syscalls.h>
 #include <linux/mempolicy.h>
 #include <linux/hugetlb.h>
+#include <linux/sched.h>
+
+/*
+ * Any behaviour which results in changes to the vma->vm_flags needs to
+ * take mmap_sem for writing. Others, which simply traverse vmas, need
+ * to only take it for reading.
+ */
+static int madvise_need_mmap_write(int behavior)
+{
+	switch (behavior) {
+	case MADV_REMOVE:
+	case MADV_WILLNEED:
+	case MADV_DONTNEED:
+		return 0;
+	default:
+		/* be safe, default to 1. list exceptions explicitly */
+		return 1;
+	}
+}
 
 /*
  * We can potentially split a vm area into separate
@@ -183,9 +202,9 @@ static long madvise_remove(struct vm_area_struct *vma,
 			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 
 	/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
-	up_write(&current->mm->mmap_sem);
+	up_read(&current->mm->mmap_sem);
 	error = vmtruncate_range(mapping->host, offset, endoff);
-	down_write(&current->mm->mmap_sem);
+	down_read(&current->mm->mmap_sem);
 	return error;
 }
 
@@ -268,9 +287,14 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
 	struct vm_area_struct * vma, *prev;
 	int unmapped_error = 0;
 	int error = -EINVAL;
+	int write;
 	size_t len;
 
-	down_write(&current->mm->mmap_sem);
+	write = madvise_need_mmap_write(behavior);
+	if (write)
+		down_write(&current->mm->mmap_sem);
+	else
+		down_read(&current->mm->mmap_sem);
 
 	if (start & ~PAGE_MASK)
 		goto out;
@@ -332,6 +356,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
 			vma = find_vma(current->mm, start);
 	}
 out:
-	up_write(&current->mm->mmap_sem);
+	if (write)
+		up_write(&current->mm->mmap_sem);
+	else
+		up_read(&current->mm->mmap_sem);
+
 	return error;
 }