From: Dave Chinner dchinner@redhat.com
maillist inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9VTE3 CVE: NA
Reference: https://lore.kernel.org/linux-xfs/20240705162450.3481169-1-john.g.garry@orac...
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When we do a large allocation, the core free space allocation code assumes that args->maxlen is aligned to args->prod/args->mod. hence if we get a maximum sized extent allocated, it does not do tail alignment of the extent.
However, this assumes that nothing modifies args->maxlen between the original allocation context setup and trimming the selected free space extent to size. This assumption has recently been found to be invalid - xfs_alloc_space_available() modifies args->maxlen in low space situations - and there may be more situations we haven't yet found like this.
Force aligned allocation introduces the requirement that extents are correctly tail aligned, resulting in this occasional latent alignment failure to be reclassified from an unimportant curiousity to a must-fix bug.
Removing the assumption about args->maxlen allocations always being tail aligned is trivial, and should not impact anything because args->maxlen for inodes with extent size hints configured are already aligned. Hence all this change does it avoid weird corner cases that would have resulted in unaligned extent sizes by always trimming the extent down to an aligned size.
Signed-off-by: Dave Chinner dchinner@redhat.com Reviewed-by: "Darrick J. Wong" djwong@kernel.org [provisional on v1 series comment] Signed-off-by: John Garry john.g.garry@oracle.com Signed-off-by: Long Li leo.lilong@huawei.com --- fs/xfs/libxfs/xfs_alloc.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c index 19d89bf19b48..23c0e666d2f4 100644 --- a/fs/xfs/libxfs/xfs_alloc.c +++ b/fs/xfs/libxfs/xfs_alloc.c @@ -408,20 +408,18 @@ xfs_alloc_compute_diff( * Fix up the length, based on mod and prod. * len should be k * prod + mod for some k. * If len is too small it is returned unchanged. - * If len hits maxlen it is left alone. */ -STATIC void +static void xfs_alloc_fix_len( - xfs_alloc_arg_t *args) /* allocation argument structure */ + struct xfs_alloc_arg *args) { - xfs_extlen_t k; - xfs_extlen_t rlen; + xfs_extlen_t k; + xfs_extlen_t rlen = args->len;
ASSERT(args->mod < args->prod); - rlen = args->len; ASSERT(rlen >= args->minlen); ASSERT(rlen <= args->maxlen); - if (args->prod <= 1 || rlen < args->mod || rlen == args->maxlen || + if (args->prod <= 1 || rlen < args->mod || (args->mod == 0 && rlen < args->prod)) return; k = rlen % args->prod;