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

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
......@@ -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;
}
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