On 11/4/21 12:00 AM, Song Liu wrote:
In some profiler use cases, it is necessary to map an address to the
backing file, e.g., a shared library. bpf_find_vma helper provides a
flexible way to achieve this. bpf_find_vma maps an address of a task to
the vma (vm_area_struct) for this address, and feed the vma to an callback
BPF function. The callback function is necessary here, as we need to
ensure mmap_sem is unlocked.
It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
safely when irqs are disable, we use the same mechanism as stackmap with
build_id. Specifically, when irqs are disabled, the unlocked is postponed
in an irq_work. Refactor stackmap.c so that the irq_work is shared among
bpf_find_vma and stackmap helpers.
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 20 ++++++++++
kernel/bpf/mmap_unlock_work.h | 65 +++++++++++++++++++++++++++++++
kernel/bpf/stackmap.c | 71 ++++++++--------------------------
kernel/bpf/task_iter.c | 49 +++++++++++++++++++++++
kernel/bpf/verifier.c | 36 +++++++++++++++++
kernel/trace/bpf_trace.c | 2 +
tools/include/uapi/linux/bpf.h | 20 ++++++++++
8 files changed, 209 insertions(+), 55 deletions(-)
create mode 100644 kernel/bpf/mmap_unlock_work.h
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2be6dfd68df99..df3410bff4b06 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2157,6 +2157,7 @@ extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;
extern const struct bpf_func_proto bpf_sk_setsockopt_proto;
extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
+extern const struct bpf_func_proto bpf_find_vma_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ba5af15e25f5c..22fa7b74de451 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4938,6 +4938,25 @@ union bpf_attr {
* **-ENOENT** if symbol is not found.
*
* **-EPERM** if caller does not have permission to obtain kernel address.
+ *
+ * long bpf_find_vma(struct task_struct *task, u64 addr, void *callback_fn, void *callback_ctx, u64 flags)
+ * Description
+ * Find vma of *task* that contains *addr*, call *callback_fn*
+ * function with *task*, *vma*, and *callback_ctx*.
+ * The *callback_fn* should be a static function and
+ * the *callback_ctx* should be a pointer to the stack.
+ * The *flags* is used to control certain aspects of the helper.
+ * Currently, the *flags* must be 0.
+ *
+ * The expected callback signature is
+ *
+ * long (\*callback_fn)(struct task_struct \*task, struct vm_area_struct \*vma, void \*ctx);
ctx => callback_ctx
this should make it clear what this 'ctx' is.
+ *
+ * Return
+ * 0 on success.
+ * **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
+ * **-EBUSY** if failed to try lock mmap_lock.
+ * **-EINVAL** for invalid **flags**.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5120,6 +5139,7 @@ union bpf_attr {
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
+ FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
[...]
+
static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
u64 *ips, u32 trace_nr, bool user)
{
- int i;
+ struct mmap_unlock_irq_work *work = NULL;
+ bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
struct vm_area_struct *vma;
- bool irq_work_busy = false;
- struct stack_map_irq_work *work = NULL;
-
- if (irqs_disabled()) {
- if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
- work = this_cpu_ptr(&up_read_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;
- }
- }
+ int i;
I think moving 'int i' is unnecessary here since there is no
functionality change.
- /*
- * We cannot do up_read() when the irq is disabled, because of
- * risk to deadlock with rq_lock. To do build_id lookup when the
- * irqs are disabled, we need to run up_read() 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 back to report ips.
- *
- * Same fallback is used for kernel stack (!user) on a stackmap
- * with build_id.
+ /* 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 (!user || !current || !current->mm || irq_work_busy ||
!mmap_read_trylock(current->mm)) {
[...]
+
+ irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
+
+ if (irq_work_busy || !mmap_read_trylock(mm))
+ return -EBUSY;
+
+ vma = find_vma(mm, start);
+
+ if (vma && vma->vm_start <= start && vma->vm_end > start) {
+ callback_fn((u64)(long)task, (u64)(long)vma,
+ (u64)(long)callback_ctx, 0, 0);
+ ret = 0;
+ }
+ bpf_mmap_unlock_mm(work, mm);
+ return ret;
+}
+
+BTF_ID_LIST_SINGLE(btf_find_vma_ids, struct, task_struct)
We have global btf_task_struct_ids, maybe reuse it?
+
+const struct bpf_func_proto bpf_find_vma_proto = {
+ .func = bpf_find_vma,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg1_btf_id = &btf_find_vma_ids[0],
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_PTR_TO_FUNC,
+ .arg4_type = ARG_PTR_TO_STACK_OR_NULL,
+ .arg5_type = ARG_ANYTHING,
+};
+
static int __init task_iter_init(void)
{
int ret;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f0dca726ebfde..a65526112924a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6132,6 +6132,35 @@ static int set_timer_callback_state(struct bpf_verifier_env *env,
return 0;
}
+BTF_ID_LIST_SINGLE(btf_set_find_vma_ids, struct, vm_area_struct)
In task_iter.c, we have
BTF_ID_LIST(btf_task_file_ids)
BTF_ID(struct, file)
BTF_ID(struct, vm_area_struct)
Maybe it is worthwhile to separate them so we can put vm_area_struct as
global to be reused.
+
+static int set_find_vma_callback_state(struct bpf_verifier_env *env,
+ struct bpf_func_state *caller,
+ struct bpf_func_state *callee,
+ int insn_idx)
+{
+ /* bpf_find_vma(struct task_struct *task, u64 start,
start => addr ?
+ * void *callback_fn, void *callback_ctx, u64 flags)
+ * (callback_fn)(struct task_struct *task,
+ * struct vm_area_struct *vma, void *ctx);
ctx => callback_ctx ?
+ */
+ callee->regs[BPF_REG_1] = caller->regs[BPF_REG_1];
+
+ callee->regs[BPF_REG_2].type = PTR_TO_BTF_ID;
+ __mark_reg_known_zero(&callee->regs[BPF_REG_2]);
+ callee->regs[BPF_REG_2].btf = btf_vmlinux;
+ callee->regs[BPF_REG_2].btf_id = btf_set_find_vma_ids[0];
+
+ /* pointer to stack or null */
+ callee->regs[BPF_REG_3] = caller->regs[BPF_REG_4];
+
+ /* unused */
+ __mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
+ __mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
+ callee->in_callback_fn = true;
+ return 0;
+}
+
[...]
