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authorRoss Zwisler <ross.zwisler@linux.intel.com>2017-05-12 15:47:00 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-05-12 15:57:16 -0700
commit876f29460cbd4086b43475890c1bf2488fa11d40 (patch)
treefc4fdd4ca0fd5d391ccab5b6aa7323800c60555f
parent13e451fdc1af05568ea379d71c02a126295d2244 (diff)
downloadlinux-stericsson-876f29460cbd4086b43475890c1bf2488fa11d40.tar.gz
dax: fix PMD data corruption when fault races with write
This is based on a patch from Jan Kara that fixed the equivalent race in the DAX PTE fault path. Currently DAX PMD read fault can race with write(2) in the following way: CPU1 - write(2) CPU2 - read fault dax_iomap_pmd_fault() ->iomap_begin() - sees hole dax_iomap_rw() iomap_apply() ->iomap_begin - allocates blocks dax_iomap_actor() invalidate_inode_pages2_range() - there's nothing to invalidate grab_mapping_entry() - we add huge zero page to the radix tree and map it to page tables The result is that hole page is mapped into page tables (and thus zeros are seen in mmap) while file has data written in that place. Fix the problem by locking exception entry before mapping blocks for the fault. That way we are sure invalidate_inode_pages2_range() call for racing write will either block on entry lock waiting for the fault to finish (and unmap stale page tables after that) or read fault will see already allocated blocks by write(2). Fixes: 9f141d6ef6258 ("dax: Call ->iomap_begin without entry lock during dax fault") Link: http://lkml.kernel.org/r/20170510172700.18991-1-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Dan Williams <dan.j.williams@intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/dax.c28
1 files changed, 14 insertions, 14 deletions
diff --git a/fs/dax.c b/fs/dax.c
index 32f020c9cedf..93ae87297ffa 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1388,6 +1388,16 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
goto fallback;
/*
+ * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX
+ * PMD or a HZP entry. If it can't (because a 4k page is already in
+ * the tree, for instance), it will return -EEXIST and we just fall
+ * back to 4k entries.
+ */
+ entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD);
+ if (IS_ERR(entry))
+ goto fallback;
+
+ /*
* Note that we don't use iomap_apply here. We aren't doing I/O, only
* setting up a mapping, so really we're using iomap_begin() as a way
* to look up our filesystem block.
@@ -1395,21 +1405,11 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
pos = (loff_t)pgoff << PAGE_SHIFT;
error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
if (error)
- goto fallback;
+ goto unlock_entry;
if (iomap.offset + iomap.length < pos + PMD_SIZE)
goto finish_iomap;
- /*
- * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX
- * PMD or a HZP entry. If it can't (because a 4k page is already in
- * the tree, for instance), it will return -EEXIST and we just fall
- * back to 4k entries.
- */
- entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD);
- if (IS_ERR(entry))
- goto finish_iomap;
-
switch (iomap.type) {
case IOMAP_MAPPED:
result = dax_pmd_insert_mapping(vmf, &iomap, pos, &entry);
@@ -1417,7 +1417,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
case IOMAP_UNWRITTEN:
case IOMAP_HOLE:
if (WARN_ON_ONCE(write))
- goto unlock_entry;
+ break;
result = dax_pmd_load_hole(vmf, &iomap, &entry);
break;
default:
@@ -1425,8 +1425,6 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
break;
}
- unlock_entry:
- put_locked_mapping_entry(mapping, pgoff, entry);
finish_iomap:
if (ops->iomap_end) {
int copied = PMD_SIZE;
@@ -1442,6 +1440,8 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf,
ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags,
&iomap);
}
+ unlock_entry:
+ put_locked_mapping_entry(mapping, pgoff, entry);
fallback:
if (result == VM_FAULT_FALLBACK) {
split_huge_pmd(vma, vmf->pmd, vmf->address);