diff options
| -rw-r--r-- | kernel/bpf/mmap_unlock_work.h | 51 | ||||
| -rw-r--r-- | kernel/bpf/stackmap.c | 28 | ||||
| -rw-r--r-- | kernel/bpf/task_iter.c | 14 |
3 files changed, 56 insertions, 37 deletions
diff --git a/kernel/bpf/mmap_unlock_work.h b/kernel/bpf/mmap_unlock_work.h index 5d18d7d85bef..1834db20b861 100644 --- a/kernel/bpf/mmap_unlock_work.h +++ b/kernel/bpf/mmap_unlock_work.h @@ -4,12 +4,15 @@ #ifndef __MMAP_UNLOCK_WORK_H__ #define __MMAP_UNLOCK_WORK_H__ +#include <linux/atomic.h> +#include <linux/err.h> #include <linux/irq_work.h> /* irq_work to run mmap_read_unlock() in irq_work */ struct mmap_unlock_irq_work { struct irq_work irq_work; struct mm_struct *mm; + atomic_t active; }; DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work); @@ -18,32 +21,36 @@ DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work); * We cannot do mmap_read_unlock() when the irq is disabled, because of * risk to deadlock with rq_lock. To look up vma when the irqs are * disabled, we need to run mmap_read_unlock() in irq_work. We use a - * percpu variable to do the irq_work. If the irq_work is already used - * by another lookup, we fall over. + * percpu variable to do the irq_work. The active flag reserves the slot + * before mmap_read_trylock() and until the irq_work callback consumes mm. */ -static inline bool bpf_mmap_unlock_get_irq_work(struct mmap_unlock_irq_work **work_ptr) +static inline struct mmap_unlock_irq_work *bpf_mmap_unlock_guard_get(void) { - struct mmap_unlock_irq_work *work = NULL; - bool irq_work_busy = false; + struct mmap_unlock_irq_work *work; - if (irqs_disabled()) { - if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { - work = this_cpu_ptr(&mmap_unlock_work); - if (irq_work_is_busy(&work->irq_work)) { - /* cannot queue more up_read, fallback */ - irq_work_busy = true; - } - } else { - /* - * PREEMPT_RT does not allow to trylock mmap sem in - * interrupt disabled context. Force the fallback code. - */ - irq_work_busy = true; - } - } + if (!irqs_disabled()) + return NULL; + + /* + * PREEMPT_RT does not allow to trylock mmap sem in interrupt + * disabled context. Force the fallback code. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return ERR_PTR(-EBUSY); + + work = this_cpu_ptr(&mmap_unlock_work); + if (irq_work_is_busy(&work->irq_work) || + atomic_cmpxchg_acquire(&work->active, 0, 1)) + return ERR_PTR(-EBUSY); - *work_ptr = work; - return irq_work_busy; + return work; +} + +static inline void +bpf_mmap_unlock_guard_put(struct mmap_unlock_irq_work *work) +{ + if (work) + atomic_set_release(&work->active, 0); } static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 8f0f3ff1a869..a839041e0d00 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -414,8 +414,7 @@ static void stack_map_get_build_id_offset_sleepable(struct bpf_stack_build_id *i static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, u32 trace_nr, bool user, bool may_fault) { - struct mmap_unlock_irq_work *work = NULL; - bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work); + struct mmap_unlock_irq_work *work; bool has_user_ctx = user && current && current->mm; struct stack_map_build_id_cache cache = {}; struct vm_area_struct *vma; @@ -426,15 +425,16 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, return; } - /* If the irq_work is in use, fall back to report ips. Same - * fallback is used for kernel stack (!user) on a stackmap with - * build_id. - */ - if (!has_user_ctx || irq_work_busy || !mmap_read_trylock(current->mm)) { - /* cannot access current->mm, fall back to ips */ - for (i = 0; i < trace_nr; i++) - stack_map_build_id_set_ip(&id_offs[i]); - return; + if (!has_user_ctx) + goto fallback; + + work = bpf_mmap_unlock_guard_get(); + if (IS_ERR(work)) + goto fallback; + + if (!mmap_read_trylock(current->mm)) { + bpf_mmap_unlock_guard_put(work); + goto fallback; } for (i = 0; i < trace_nr; i++) { @@ -465,6 +465,12 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, vma->vm_pgoff); } bpf_mmap_unlock_mm(work, current->mm); + return; + +fallback: + /* cannot access current->mm, fall back to ips */ + for (i = 0; i < trace_nr; i++) + stack_map_build_id_set_ip(&id_offs[i]); } static struct perf_callchain_entry * diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index b256fb9c1214..13e1aabe6f88 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -753,9 +753,8 @@ static struct bpf_iter_reg task_vma_reg_info = { BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, bpf_callback_t, callback_fn, void *, callback_ctx, u64, flags) { - struct mmap_unlock_irq_work *work = NULL; + struct mmap_unlock_irq_work *work; struct vm_area_struct *vma; - bool irq_work_busy = false; bool __maybe_unused mmput_needed = false; struct mm_struct *mm; int ret = -ENOENT; @@ -792,9 +791,14 @@ BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, if (!mm) return -ENOENT; - irq_work_busy = bpf_mmap_unlock_get_irq_work(&work); + work = bpf_mmap_unlock_guard_get(); + if (IS_ERR(work)) { + ret = PTR_ERR(work); + goto out; + } - if (irq_work_busy || !mmap_read_trylock(mm)) { + if (!mmap_read_trylock(mm)) { + bpf_mmap_unlock_guard_put(work); ret = -EBUSY; goto out; } @@ -1191,6 +1195,8 @@ static void do_mmap_read_unlock(struct irq_work *entry) work = container_of(entry, struct mmap_unlock_irq_work, irq_work); mmap_read_unlock_non_owner(work->mm); + work->mm = NULL; + bpf_mmap_unlock_guard_put(work); } static int __init task_iter_init(void) |