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[PATCH] holepunch: fix mmap_sem i_mutex deadlock

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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>
This commit is contained in:
Hugh Dickins 2007-03-29 01:20:38 -07:00 committed by Linus Torvalds
parent 16a100190d
commit 90ed52ebe4
1 changed files with 14 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

19
mm/madvise.c
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@ -159,9 +159,10 @@ static long madvise_remove(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
struct address_space *mapping;
loff_t offset, endoff;
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;
vma = prev->vm_next;
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);