Re: [PATCH v4 32/38] mm/madvise: use predicates for madvise(..., MADV_DOFORK)
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From: sashiko-bot@kernel.org
Date: 2026-10-03 17:57:13
Also in:
bpf, dri-devel, kvm, kvmarm, linux-perf-users, linux-rdma, linux-s390, linux-scsi, selinux
Make it clear what we're blocking in MADV_DOFORK. Previously we simply
disallowed VM_SPECIAL i.e. mappings not managed by core mm, fixed mappings
and
VMA_IO_BIT.
Now the invariant is established that mm-managed mappings may not set
VMA_IO_BIT, the VMA_IO_BIT check is redundant.
The rest is equivalent to testing for a fixed or non-mm-managed 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.
Acked-by: Zi Yan <ziy@nvidia.com>
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/20261003-b4-mmap-prepare-vma-flag-sanify-v4-0-a1f052500fd7@kernel.org?part=32