Re: [PATCH v3 33/40] mm/madvise: use predicates for madvise(..., MADV_DOFORK)
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From: "Zi Yan" <ziy@nvidia.com>
Date: 2026-09-30 02:28:38
Also in:
bpf, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fbdev, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
On Thu Sep 17, 2026 at 12:22 PM EDT, Lorenzo Stoakes (ARM) wrote:
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>
---
mm/madvise.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)Makes sense. Acked-by: Zi Yan <ziy@nvidia.com> -- Best Regards, Yan, Zi