The patch titled
Subject: dax: fix deadlock in __dax_fault()
has been added to the -mm tree. Its filename is
dax-fix-deadlock-in-__dax_fault.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dax-fix-deadlock-in-__dax_fault.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dax-fix-deadlock-in-__dax_fault.patch
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: dax: fix deadlock in __dax_fault()
Fix the deadlock exposed by xfstests generic/075. Here is the sequence
that was causing us to deadlock:
1) enter __dax_fault()
2) page = find_get_page() gives us a page, so skip
i_mmap_lock_write(mapping)
3) if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page)
passes, enter this block
4) if (vmf->flags & FAULT_FLAG_WRITE) fails, so do the else case and
i_mmap_unlock_write(mapping);
return dax_load_hole(mapping, page, vmf);
This causes us to up_write() a semaphore that we weren't holding.
The up_write() on a semaphore we didn't down_write() happens twice in
a row, and then the next time we try and i_mmap_lock_write(), we hang.
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reported-by: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN fs/dax.c~dax-fix-deadlock-in-__dax_fault fs/dax.c
--- a/fs/dax.c~dax-fix-deadlock-in-__dax_fault
+++ a/fs/dax.c
@@ -405,7 +405,8 @@ int __dax_fault(struct vm_area_struct *v
if (error)
goto unlock;
} else {
- i_mmap_unlock_write(mapping);
+ if (!page)
+ i_mmap_unlock_write(mapping);
return dax_load_hole(mapping, page, vmf);
}
}
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
dax-fix-null-pointer-in-__dax_pmd_fault.patch
dax-fix-deadlock-in-__dax_fault.patch
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