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Commit 0a27a14a authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

mm: madvise avoid exclusive mmap_sem 



Avoid down_write of the mmap_sem in madvise when we can help it.

Acked-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b4169525

mm/madvise.c

+29 −4
Original line number Diff line number Diff line
@@ -11,6 +11,24 @@ 
#include <linux/mempolicy.h>

#include <linux/hugetlb.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

 * areas, each area with its own behavior.
@@ -183,9 +201,9 @@ 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;

}
@@ -270,7 +288,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior) 
	int error = -EINVAL;

	size_t len;



	if (madvise_need_mmap_write(behavior))

		down_write(&current->mm->mmap_sem);

	else

		down_read(&current->mm->mmap_sem);



	if (start & ~PAGE_MASK)

		goto out;
@@ -332,6 +353,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior) 
			vma = find_vma(current->mm, start);

	}

out:

	if (madvise_need_mmap_write(behavior))

		up_write(&current->mm->mmap_sem);

	else

		up_read(&current->mm->mmap_sem);



	return error;

}