1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 /* Copyright (c) 2021 Facebook 3 */ 4 5 #ifndef __MMAP_UNLOCK_WORK_H__ 6 #define __MMAP_UNLOCK_WORK_H__ 7 #include <linux/irq_work.h> 8 9 /* irq_work to run mmap_read_unlock() in irq_work */ 10 struct mmap_unlock_irq_work { 11 struct irq_work irq_work; 12 struct mm_struct *mm; 13 }; 14 15 DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work); 16 17 /* 18 * We cannot do mmap_read_unlock() when the irq is disabled, because of 19 * risk to deadlock with rq_lock. To look up vma when the irqs are 20 * disabled, we need to run mmap_read_unlock() in irq_work. We use a 21 * percpu variable to do the irq_work. If the irq_work is already used 22 * by another lookup, we fall over. 23 */ 24 static inline bool bpf_mmap_unlock_get_irq_work(struct mmap_unlock_irq_work **work_ptr) 25 { 26 struct mmap_unlock_irq_work *work = NULL; 27 bool irq_work_busy = false; 28 29 if (irqs_disabled()) { 30 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { 31 work = this_cpu_ptr(&mmap_unlock_work); 32 if (irq_work_is_busy(&work->irq_work)) { 33 /* cannot queue more up_read, fallback */ 34 irq_work_busy = true; 35 } 36 } else { 37 /* 38 * PREEMPT_RT does not allow to trylock mmap sem in 39 * interrupt disabled context. Force the fallback code. 40 */ 41 irq_work_busy = true; 42 } 43 } 44 45 *work_ptr = work; 46 return irq_work_busy; 47 } 48 49 static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm) 50 { 51 if (!work) { 52 mmap_read_unlock(mm); 53 } else { 54 work->mm = mm; 55 56 /* The lock will be released once we're out of interrupt 57 * context. Tell lockdep that we've released it now so 58 * it doesn't complain that we forgot to release it. 59 */ 60 rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_); 61 irq_work_queue(&work->irq_work); 62 } 63 } 64 65 #endif /* __MMAP_UNLOCK_WORK_H__ */ 66