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authorHugh Dickins <hugh@veritas.com>2007-04-13 18:27:55 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2007-05-01 17:05:56 -0700
commit64f586d81ecc913a557055d4804c987f8c766888 (patch)
tree9fa41d46aa20c9cbf3d583cd2cdefaf4c90cdaa7
parent42988ea6a81e888a6aa28549071e00400b68f4f7 (diff)
holepunch: fix mmap_sem i_mutex deadlock
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--mm/madvise.c19
1 files changed, 14 insertions, 5 deletions
diff --git a/mm/madvise.c b/mm/madvise.c
index 77916e9fc52b..603c5257ed6e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -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);