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authorJan Kara <jack@suse.cz>2017-05-12 15:46:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-05-12 15:57:16 -0700
commit13e451fdc1af05568ea379d71c02a126295d2244 (patch)
treee2305568ef383361e88607860d4a73a31213a7d1
parentfb26a1cbed8c90025572d48bc9eabe59f7571e88 (diff)
downloadlinux-stericsson-13e451fdc1af05568ea379d71c02a126295d2244.tar.gz
dax: fix data corruption when fault races with write
Currently DAX read fault can race with write(2) in the following way: CPU1 - write(2) CPU2 - read fault dax_iomap_pte_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 zero page in 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: 9f141d6ef6258a3a37a045842d9ba7e68f368956 Link: http://lkml.kernel.org/r/20170510085419.27601-5-jack@suse.cz Signed-off-by: Jan Kara <jack@suse.cz> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> 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.c32
1 files changed, 16 insertions, 16 deletions
diff --git a/fs/dax.c b/fs/dax.c
index 123d9903c77d..32f020c9cedf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1148,6 +1148,12 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
flags |= IOMAP_WRITE;
+ entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
+ if (IS_ERR(entry)) {
+ vmf_ret = dax_fault_return(PTR_ERR(entry));
+ goto out;
+ }
+
/*
* Note that we don't bother to use iomap_apply here: DAX required
* the file system block size to be equal the page size, which means
@@ -1156,17 +1162,11 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
if (error) {
vmf_ret = dax_fault_return(error);
- goto out;
+ goto unlock_entry;
}
if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
- vmf_ret = dax_fault_return(-EIO); /* fs corruption? */
- goto finish_iomap;
- }
-
- entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
- if (IS_ERR(entry)) {
- vmf_ret = dax_fault_return(PTR_ERR(entry));
- goto finish_iomap;
+ error = -EIO; /* fs corruption? */
+ goto error_finish_iomap;
}
sector = dax_iomap_sector(&iomap, pos);
@@ -1188,13 +1188,13 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
}
if (error)
- goto error_unlock_entry;
+ goto error_finish_iomap;
__SetPageUptodate(vmf->cow_page);
vmf_ret = finish_fault(vmf);
if (!vmf_ret)
vmf_ret = VM_FAULT_DONE_COW;
- goto unlock_entry;
+ goto finish_iomap;
}
switch (iomap.type) {
@@ -1214,7 +1214,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
case IOMAP_HOLE:
if (!(vmf->flags & FAULT_FLAG_WRITE)) {
vmf_ret = dax_load_hole(mapping, &entry, vmf);
- goto unlock_entry;
+ goto finish_iomap;
}
/*FALLTHRU*/
default:
@@ -1223,10 +1223,8 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
break;
}
- error_unlock_entry:
+ error_finish_iomap:
vmf_ret = dax_fault_return(error) | major;
- unlock_entry:
- put_locked_mapping_entry(mapping, vmf->pgoff, entry);
finish_iomap:
if (ops->iomap_end) {
int copied = PAGE_SIZE;
@@ -1241,7 +1239,9 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
*/
ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap);
}
-out:
+ unlock_entry:
+ put_locked_mapping_entry(mapping, vmf->pgoff, entry);
+ out:
trace_dax_pte_fault_done(inode, vmf, vmf_ret);
return vmf_ret;
}