[PATCH v6 05/14] mm: clarify lazy_mmu sleeping constraints
From: Kevin Brodsky <hidden>
Date: 2025-12-15 15:04:05
Also in:
linux-arm-kernel, linux-mm, lkml, sparclinux, xen-devel
Subsystem:
memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
The lazy MMU mode documentation makes clear that an implementation should not assume that preemption is disabled or any lock is held upon entry to the mode; however it says nothing about what code using the lazy MMU interface should expect. In practice sleeping is forbidden (for generic code) while the lazy MMU mode is active: say it explicitly. Signed-off-by: Kevin Brodsky <redacted> --- include/linux/pgtable.h | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 652f287c1ef6..1abc4a1c3d72 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h@@ -225,11 +225,15 @@ static inline int pmd_dirty(pmd_t pmd) * up to date. * * In the general case, no lock is guaranteed to be held between entry and exit - * of the lazy mode. So the implementation must assume preemption may be enabled - * and cpu migration is possible; it must take steps to be robust against this. - * (In practice, for user PTE updates, the appropriate page table lock(s) are - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted - * and the mode cannot be used in interrupt context. + * of the lazy mode. (In practice, for user PTE updates, the appropriate page + * table lock(s) are held, but for kernel PTE updates, no lock is held). + * The implementation must therefore assume preemption may be enabled upon + * entry to the mode and cpu migration is possible; it must take steps to be + * robust against this. An implementation may handle this by disabling + * preemption, as a consequence generic code may not sleep while the lazy MMU + * mode is active. + * + * Nesting is not permitted and the mode cannot be used in interrupt context. */ #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE static inline void arch_enter_lazy_mmu_mode(void) {}
--
2.51.2