From 43e12263e1af715ca8b5d1c3cbb5392b58909656 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Fri, 10 Mar 2023 17:29:05 +0100 Subject: [PATCH 53/64] io-mapping: don't disable preempt on RT in io_mapping_map_atomic_wc(). io_mapping_map_atomic_wc() disables preemption and pagefaults for historical reasons. The conversion to io_mapping_map_local_wc(), which only disables migration, cannot be done wholesale because quite some call sites need to be updated to accommodate with the changed semantics. On PREEMPT_RT enabled kernels the io_mapping_map_atomic_wc() semantics are problematic due to the implicit disabling of preemption which makes it impossible to acquire 'sleeping' spinlocks within the mapped atomic sections. PREEMPT_RT replaces the preempt_disable() with a migrate_disable() for more than a decade. It could be argued that this is a justification to do this unconditionally, but PREEMPT_RT covers only a limited number of architectures and it disables some functionality which limits the coverage further. Limit the replacement to PREEMPT_RT for now. This is also done kmap_atomic(). Link: https://lkml.kernel.org/r/20230310162905.O57Pj7hh@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reported-by: Richard Weinberger <richard.weinberger@gmail.com> Link: https://lore.kernel.org/CAFLxGvw0WMxaMqYqJ5WgvVSbKHq2D2xcXTOgMCpgq9nDC-MWTQ@mail.gmail.com Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> (cherry picked from commit 7eb16f23b9a415f062db22739e59bb144e0b24ab) Signed-off-by: Clark Williams <clark.williams@gmail.com> --- include/linux/io-mapping.h | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) Index: linux-6.1.96-rt35/include/linux/io-mapping.h =================================================================== @ linux-6.1.96-rt35/include/linux/io-mapping.h:72 @ io_mapping_map_atomic_wc(struct io_mappi BUG_ON(offset >= mapping->size); phys_addr = mapping->base + offset; - preempt_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); + else + migrate_disable(); pagefault_disable(); return __iomap_local_pfn_prot(PHYS_PFN(phys_addr), mapping->prot); } @ linux-6.1.96-rt35/include/linux/io-mapping.h:85 @ io_mapping_unmap_atomic(void __iomem *va { kunmap_local_indexed((void __force *)vaddr); pagefault_enable(); - preempt_enable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); + else + migrate_enable(); } static inline void __iomem * @ linux-6.1.96-rt35/include/linux/io-mapping.h:171 @ static inline void __iomem * io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset) { - preempt_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); + else + migrate_disable(); pagefault_disable(); return io_mapping_map_wc(mapping, offset, PAGE_SIZE); } @ linux-6.1.96-rt35/include/linux/io-mapping.h:184 @ io_mapping_unmap_atomic(void __iomem *va { io_mapping_unmap(vaddr); pagefault_enable(); - preempt_enable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); + else + migrate_enable(); } static inline void __iomem *