Re: [PATCH v2 33/40] mm/madvise: use predicates for madvise(..., MADV_DOFORK)
From: sashiko-bot@kernel.org
Date: 2026-09-14 22:18:10
Also in:
bpf, dri-devel, kvm, kvmarm, linux-rdma, linux-s390, linux-scsi, linux-trace-kernel, selinux
Make it clear what we're blocking in MADV_DOFORK. Previously we simply
disallowed VM_SPECIAL i.e. kernel-owned mappings, fixed mappings and
VMA_IO_BIT.
Now the invariant is established that only kernel-owned mappings can set
VMA_IO_BIT, the VMA_IO_BIT check is redundant.
The rest is equivalent to testing for a kernel-owned or fixed mapping,
i.e. exactly the same check as whether the VMA is permitted to be merged.
This was established by commit 0b2758f48f22 ("Require (reasonably) normal
mappings for MADV_DOFORK") containing my hands-down favourite call out of
all time.
Express the same thing differently - if we wouldn't be allowed to merge it,
then we aren't allowed to manipulate CoW behaviour on fork.
No functional change intended.
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>Sashiko has reviewed this patch and found no issues. It looks great! -- Sashiko AI review · https://sashiko.dev/#/patchset/20260914-b4-mmap-prepare-vma-flag-sanify-v2-0-7d9781ed5361@kernel.org?part=33