From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> gup_pgd_range() is invoked with disabled interrupts and invokes __kmap_local_page_prot() via pte_offset_map(), gup_p4d_range(). With HIGHPTE enabled, __kmap_local_page_prot() invokes kmap_high_get() which uses a spinlock_t via lock_kmap_any(). This leads to an sleeping-while-atomic error on PREEMPT_RT because spinlock_t becomes a sleeping lock and must not be acquired in atomic context. The loop in map_new_virtual() uses wait_queue_head_t for wake up which also is using a spinlock_t. Since HIGHPTE is rarely needed at all, turn it off for PREEMPT_RT to allow the use of get_user_pages_fast(). [arnd: rework patch to turn off HIGHPTE instead of HAVE_PAST_GUP] Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- There is an open question about whether HIGHPTE is still needed at all, given how rare 32-bit machines with more than 4GB are on any architecture. If we instead decide to remove HIGHPTE altogether, this patch is no longer needed. --- arch/arm/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index ed850cc0ed3c..4de4e5697bdf 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1231,7 +1231,7 @@ config HIGHMEM config HIGHPTE bool "Allocate 2nd-level pagetables from highmem" if EXPERT - depends on HIGHMEM + depends on HIGHMEM && !PREEMPT_RT default y help The VM uses one page of physical memory for each page table. -- 2.39.5
