[PATCH] holepunch: fix mmap_sem i_mutex deadlock (90ed52eb) · Commits · 戴 / test

sys_madvise has down_write of mmap_sem, then madvise_remove calls vmtruncate_range which takes i_mutex and i_alloc_sem: no, we can easily devise deadlocks from that ordering. madvise_remove drop mmap_sem while calling vmtruncate_range: luckily, since madvise_remove doesn't split or merge vmas, it's easy to handle this case with a NULL prev, without restructuring sys_madvise. (Though sad to retake mmap_sem when it's unlikely to be needed, and certainly down_read is sufficient for MADV_REMOVE, unlike the other madvices.) Signed-off-by:

Hugh Dickins <hugh@veritas.com> Cc: Miklos Szeredi <mszeredi@suse.cz> Cc: Badari Pulavarty <pbadari@us.ibm.com> Cc: Nick Piggin <npiggin@suse.de> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/madvise.c

+14 −5

Original line number	Diff line number	Diff line
		@@ -160,8 +160,9 @@ static long madvise_remove(struct vm_area_struct *vma,
		{
		struct address_space *mapping;
		loff_t offset, endoff;
		int error;

		*prev = vma;
		prev = NULL; / tell sys_madvise we drop mmap_sem */

		if (vma->vm_flags & (VM_LOCKED\|VM_NONLINEAR\|VM_HUGETLB))
		return -EINVAL;
		@@ -180,7 +181,12 @@ static long madvise_remove(struct vm_area_struct *vma,
		+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
		endoff = (loff_t)(end - vma->vm_start - 1)
		+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
		return vmtruncate_range(mapping->host, offset, endoff);

		/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
		up_write(&current->mm->mmap_sem);
		error = vmtruncate_range(mapping->host, offset, endoff);
		down_write(&current->mm->mmap_sem);
		return error;
		}

		static long
		@@ -315,12 +321,15 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
		if (error)
		goto out;
		start = tmp;
		if (start < prev->vm_end)
		if (prev && start < prev->vm_end)
		start = prev->vm_end;
		error = unmapped_error;
		if (start >= end)
		goto out;
		if (prev)
		vma = prev->vm_next;
		else /* madvise_remove dropped mmap_sem */
		vma = find_vma(current->mm, start);
		}
		out:
		up_write(&current->mm->mmap_sem);

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