From 81438498a285759f31e843ac4800f82a5ce6521f Mon Sep 17 00:00:00 2001 From: Sergey Bashirov Date: Tue, 1 Jul 2025 15:21:48 +0300 Subject: [PATCH] pNFS: Fix stripe mapping in block/scsi layout Because of integer division, we need to carefully calculate the disk offset. Consider the example below for a stripe of 6 volumes, a chunk size of 4096, and an offset of 70000. chunk = div_u64(offset, dev->chunk_size) = 70000 / 4096 = 17 offset = chunk * dev->chunk_size = 17 * 4096 = 69632 disk_offset_wrong = div_u64(offset, dev->nr_children) = 69632 / 6 = 11605 disk_chunk = div_u64(chunk, dev->nr_children) = 17 / 6 = 2 disk_offset = disk_chunk * dev->chunk_size = 2 * 4096 = 8192 Signed-off-by: Sergey Bashirov Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/r/20250701122341.199112-1-sergeybashirov@gmail.com Signed-off-by: Trond Myklebust --- fs/nfs/blocklayout/dev.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c index cab8809f0e0f..44306ac22353 100644 --- a/fs/nfs/blocklayout/dev.c +++ b/fs/nfs/blocklayout/dev.c @@ -257,10 +257,11 @@ static bool bl_map_stripe(struct pnfs_block_dev *dev, u64 offset, struct pnfs_block_dev *child; u64 chunk; u32 chunk_idx; + u64 disk_chunk; u64 disk_offset; chunk = div_u64(offset, dev->chunk_size); - div_u64_rem(chunk, dev->nr_children, &chunk_idx); + disk_chunk = div_u64_rem(chunk, dev->nr_children, &chunk_idx); if (chunk_idx >= dev->nr_children) { dprintk("%s: invalid chunk idx %d (%lld/%lld)\n", @@ -273,7 +274,7 @@ static bool bl_map_stripe(struct pnfs_block_dev *dev, u64 offset, offset = chunk * dev->chunk_size; /* disk offset of the stripe */ - disk_offset = div_u64(offset, dev->nr_children); + disk_offset = disk_chunk * dev->chunk_size; child = &dev->children[chunk_idx]; child->map(child, disk_offset, map); -- 2.47.2