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mm: madvise avoid exclusive mmap_sem
Avoid down_write of the mmap_sem in madvise when we can help it. Acked-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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33
mm/madvise.c
33
mm/madvise.c
@ -11,6 +11,24 @@
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#include <linux/mempolicy.h>
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#include <linux/hugetlb.h>
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/*
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* Any behaviour which results in changes to the vma->vm_flags needs to
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* take mmap_sem for writing. Others, which simply traverse vmas, need
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* to only take it for reading.
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*/
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static int madvise_need_mmap_write(int behavior)
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{
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switch (behavior) {
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case MADV_REMOVE:
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case MADV_WILLNEED:
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case MADV_DONTNEED:
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return 0;
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default:
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/* be safe, default to 1. list exceptions explicitly */
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return 1;
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}
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}
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/*
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* We can potentially split a vm area into separate
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* areas, each area with its own behavior.
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@ -183,9 +201,9 @@ static long madvise_remove(struct vm_area_struct *vma,
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
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up_write(¤t->mm->mmap_sem);
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up_read(¤t->mm->mmap_sem);
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error = vmtruncate_range(mapping->host, offset, endoff);
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down_write(¤t->mm->mmap_sem);
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down_read(¤t->mm->mmap_sem);
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return error;
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}
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@ -270,7 +288,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
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int error = -EINVAL;
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size_t len;
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down_write(¤t->mm->mmap_sem);
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if (madvise_need_mmap_write(behavior))
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down_write(¤t->mm->mmap_sem);
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else
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down_read(¤t->mm->mmap_sem);
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if (start & ~PAGE_MASK)
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goto out;
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@ -332,6 +353,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
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vma = find_vma(current->mm, start);
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}
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out:
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up_write(¤t->mm->mmap_sem);
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if (madvise_need_mmap_write(behavior))
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up_write(¤t->mm->mmap_sem);
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else
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up_read(¤t->mm->mmap_sem);
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return error;
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}
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