__write_sb_page() rounds up the io size to the optimal io size if it
doesn't exceed the data offset, but it doesn't check the final size
exceeds the bitmap length.
For example:
page count - 1
page size - 4K
data offset - 1M
optimal io size - 256K
The final io size would be 256K (64 pages) but md_bitmap_storage_alloc()
allocated 1 page, the IO would write 1 valid page and 63 pages that
happens to be allocated afterwards. This leaks memory to the raid device
superblock.
This issue caused a data transfer failure in nvme-tcp. The network
drivers checks the first page of an IO with sendpage_ok(), it returns
true if the page isn't a slabpage and refcount >= 1. If the page
!sendpage_ok() the network driver disables MSG_SPLICE_PAGES.
As of now the network layer assumes all the pages of the IO are
sendpage_ok() when MSG_SPLICE_PAGES is on.
The bitmap pages aren't slab pages, the first page of the IO is
sendpage_ok(), but the additional pages that happens to be allocated
after the bitmap pages might be !sendpage_ok(). That cause
skb_splice_from_iter() to stop the data transfer, in the case below it
hangs 'mdadm --create'.
The bug is reproducible, in order to reproduce we need nvme-over-tcp
controllers with optimal IO size bigger than PAGE_SIZE. Creating a raid
with bitmap over those devices reproduces the bug.
In order to simulate large optimal IO size you can use dm-stripe with a
single device.
Script to reproduce the issue on top of brd devices using dm-stripe is
attached below (will be added to blktest).
I have added some logs to test the theory:
...
md: created bitmap (1 pages) for device md127
__write_sb_page before md_super_write offset: 16, size: 262144. pfn: 0x53ee
=== __write_sb_page before md_super_write. logging pages ===
pfn: 0x53ee, slab: 0 <-- the only page that allocated for the bitmap
pfn: 0x53ef, slab: 1
pfn: 0x53f0, slab: 0
pfn: 0x53f1, slab: 0
pfn: 0x53f2, slab: 0
pfn: 0x53f3, slab: 1
...
nvme_tcp: sendpage_ok - pfn: 0x53ee, len: 262144, offset: 0
skbuff: before sendpage_ok() - pfn: 0x53ee
skbuff: before sendpage_ok() - pfn: 0x53ef
WARNING at net/core/skbuff.c:6848 skb_splice_from_iter+0x142/0x450
skbuff: !sendpage_ok - pfn: 0x53ef. is_slab: 1, page_count: 1
...
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Ofir Gal <ofir.gal@xxxxxxxxxxx>
---
Changelog:
v2, split bitmap_limit line after "<<", removed pointless case, add
Christoph Hellwig review tag.
drivers/md/md-bitmap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 0a2d37eb38ef..08232d8dc815 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -227,6 +227,8 @@ static int __write_sb_page(struct md_rdev *rdev, struct bitmap *bitmap,
struct block_device *bdev;
struct mddev *mddev = bitmap->mddev;
struct bitmap_storage *store = &bitmap->storage;
+ unsigned int bitmap_limit = (bitmap->storage.file_pages - pg_index) <<
+ PAGE_SHIFT;
loff_t sboff, offset = mddev->bitmap_info.offset;
sector_t ps = pg_index * PAGE_SIZE / SECTOR_SIZE;
unsigned int size = PAGE_SIZE;
@@ -269,11 +271,9 @@ static int __write_sb_page(struct md_rdev *rdev, struct bitmap *bitmap,
if (size == 0)
/* bitmap runs in to data */
return -EINVAL;
- } else {
- /* DATA METADATA BITMAP - no problems */
}
- md_super_write(mddev, rdev, sboff + ps, (int) size, page);
+ md_super_write(mddev, rdev, sboff + ps, (int)min(size, bitmap_limit), page);
return 0;
}
--
2.45.1
