FAILED: patch "[PATCH] dax: fix data corruption when fault races with write" failed to apply to 4.10-stable tree

PATCH [email protected] 2 participants 2 messages May 18, 2017

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2017-05-18 07:26 UTC #0 lore raw

The patch below does not apply to the 4.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 13e451fdc1af05568ea379d71c02a126295d2244 Mon Sep 17 00:00:00 2001

From: Jan Kara <[email protected]>
Date: Fri, 12 May 2017 15:46:57 -0700
Subject: [PATCH] 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/[email protected] open here

Signed-off-by Jan Kara <[email protected]>

Reviewed-by Ross Zwisler <[email protected]>

Cc Dan Williams <[email protected]>

Cc <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Signed-off-by Linus Torvalds <[email protected]>

fs/dax.c +16 ~~-16~~

index 123d9903c77d..32f020c9cedf 100644
@@ -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;
 }

Ross Zwisler

Reviewed-by

2017-05-18 23:20 UTC #1 lore raw

Quoted 9 lines · On Thu, May 18, 2017 at 09:26:08AM +0200, [email protected] wrote:

The patch below does not apply to the 4.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks,
greg k-h

The following patch from Jan was sent in v3 of his series before he had merged with my tracepoint changes, and applies cleanly to v4.10.6. This is for the following upstream commit:

commit 13e451fdc1af ("dax: fix data corruption when fault races with write")

This patch relies on the previous patch in the series to work correctly, so you'll need to wait for Jan to backport that before applying this one. Here's the commit you need from Jan:

commit fb26a1cbed8c ("ext4: return to starting transaction in ext4_dax_huge_fault()")

I'll send you a backport for patch 5 in that series tomorrow, a backport of this commit:

commit 876f29460cbd ("dax: fix PMD data corruption when fault races with write")

Obviously no need to wait for that one before applying this one. :)

--- >8 ---

Quoted 1 line

From a9336fe67e892da2fc167e60db6d6069b0a786b1 Mon Sep 17 00:00:00 2001

From: Jan Kara <[email protected]>
Date: Tue, 9 May 2017 14:18:37 +0200
Subject: [PATCH] dax: Fix data corruption when fault races with write