-- Dave Chinner david@fromorbit.com xfs: fix livelock in delayed allocation at ENOSPC From: Dave Chinner dchinner@redhat.com On a filesystem with a non-zero stripe unit and a large sequential write, delayed allocation will set a minimum allocation length of the stripe unit. If allocation fails because there are no extents long enough for an aligned minlen allocation, it is supposed to fall back to unaligned allocation which allows single block extents to be allocated. When the allocator code was rewritting in the 6.3 cycle, this fallback was broken - the old code used args->fsbno as the both the allocation target and the allocation result, the new code passes the target as a separate parameter. The conversion didn't handle the aligned->unaligned fallback path correctly - it reset args->fsbno to the target fsbno on failure which broke allocation failure detection in the high level code and so it never fell back to unaligned allocations. This resulted in a loop in writeback trying to allocate an aligned block, getting a false positive success, trying to insert the result in the BMBT. This did nothing because the extent already was in the BMBT (merge results in an unchanged extent) and so it returned the prior extent to the conversion code as the current iomap. Because the iomap returned didn't cover the offset we tried to map, xfs_convert_blocks() then retries the allocation, which fails in the same way and now we have a livelock. Reported-and-tested-by: Brian Foster bfoster@redhat.com Fixes: 85843327094f ("xfs: factor xfs_bmap_btalloc()") Signed-off-by: Dave Chinner dchinner@redhat.com Reviewed-by: Darrick J. Wong djwong@kernel.org --- diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index 1a4e446194dd..b512de0540d5 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -3540,7 +3540,6 @@ xfs_bmap_btalloc_at_eof( * original non-aligned state so the caller can proceed on allocation * failure as if this function was never called. */ - args->fsbno = ap->blkno; args->alignment = 1; return 0; }