From b05a67615b982cfaa903df8a6fb055d18ebafe11 Mon Sep 17 00:00:00 2001 From: Matthias Goergens Date: Sun, 4 Oct 2026 17:56:08 +0800 Subject: [PATCH] ntfs: do not give a contiguous cluster allocation a second run ntfs_attr_map_cluster() asks ntfs_cluster_alloc() for contiguous clusters and merges the whole result into the runlist, but reports only its first run, so its callers zero only that run. Within a bitmap page the allocator keeps such a request to one run, because a cluster in use ends it. The zone search can also move on without testing the clusters after the run, though: it skips a bitmap page that has no free clusters, it goes from the end of the zone to the start of pass 2, and once every zone has been searched it shrinks the MFT zone by half and goes on at its new end. After each of these jumps the first cluster tested is still taken as the next one of the run, and if it is free it starts a second run elsewhere on the volume. fallocate() over a hole then leaves the clusters of that second run holding whatever they held before: on a nearly full volume, 16 of 20 fallocated clusters read back a deleted file's data, in each of the three cases. Delayed allocation gets a second run without punching any holes: filling the same volume with write() reaches the last case when the MFT zone is shrunk. The allocator then takes only the first run off the dirty-cluster count, and after the fill statfs() reported no free space while 939 clusters were still free, until the next mount. Before setting the bit of a cluster for a contiguous request, check that the cluster comes right after the run, and return the run as it is if not; no bit has to be cleared. ntfs_attr_map_cluster() already handles a short run, which a cluster in use produces in the same way: its callers ask again for the rest. Fixes: 11ccc9107dc4 ("ntfs: update runlist handling and cluster allocator") Suggested-by: Namjae Jeon Link: https://lore.kernel.org/all/CAKYAXd-agPFvDj2-HvjP3SLtG7AxkqUeNPqYyrLt-BN7fT8w6g@mail.gmail.com/ Signed-off-by: Matthias Goergens Signed-off-by: Namjae Jeon --- fs/ntfs/lcnalloc.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/ntfs/lcnalloc.c b/fs/ntfs/lcnalloc.c index c58e689fb585..3ebcac4c2864 100644 --- a/fs/ntfs/lcnalloc.c +++ b/fs/ntfs/lcnalloc.c @@ -375,6 +375,16 @@ struct runlist_element *ntfs_cluster_alloc(struct ntfs_volume *vol, const s64 st has_guess = 1; continue; } + /* + * A contiguous request gets a single run. The scan can + * move on without testing the clusters after the run + * (past a bitmap page that is full, to pass 2 or to + * another zone), so return the run when this cluster + * does not follow it. + */ + if (is_contig && rlpos && + lcn + bmp_pos != prev_lcn + prev_run_len) + goto out; /* * Allocate more memory if needed, including space for * the terminator element.