On 1/6/21 8:17 PM, Song Liu wrote:
Introduce task_vma bpf_iter to print memory information of a process. It
can be used to print customized information similar to /proc/<pid>/maps.
Current /proc/<pid>/maps and /proc/<pid>/smaps provide information of
vma's of a process. However, these information are not flexible enough to
cover all use cases. For example, if a vma cover mixed 2MB pages and 4kB
pages (x86_64), there is no easy way to tell which address ranges are
backed by 2MB pages. task_vma solves the problem by enabling the user to
generate customize information based on the vma (and vma->vm_mm,
vma->vm_file, etc.).
To access the vma safely in the BPF program, task_vma iterator holds
target mmap_lock while calling the BPF program. If the mmap_lock is
contended, task_vma unlocks mmap_lock between iterations to unblock the
writer(s). This lock contention avoidance mechanism is similar to the one
used in show_smaps_rollup().
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
kernel/bpf/task_iter.c | 211 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 210 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 0458a40edf10a..a1d3c9d230f68 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -304,9 +304,192 @@ static const struct seq_operations task_file_seq_ops = {
.show = task_file_seq_show,
};
+struct bpf_iter_seq_task_vma_info {
+ /* The first field must be struct bpf_iter_seq_task_common.
+ * this is assumed by {init, fini}_seq_pidns() callback functions.
+ */
+ struct bpf_iter_seq_task_common common;
+ struct task_struct *task;
+ struct vm_area_struct *vma;
+ u32 tid;
+ unsigned long prev_vm_start;
+ unsigned long prev_vm_end;
+};
+
+enum bpf_task_vma_iter_find_op {
+ task_vma_iter_first_vma, /* use mm->mmap */
+ task_vma_iter_next_vma, /* use curr_vma->vm_next */
+ task_vma_iter_find_vma, /* use find_vma() to find next vma */
+};
+
+static struct vm_area_struct *
+task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
+{
+ struct pid_namespace *ns = info->common.ns;
+ enum bpf_task_vma_iter_find_op op;
+ struct vm_area_struct *curr_vma;
+ struct task_struct *curr_task;
+ u32 curr_tid = info->tid;
+
+ /* If this function returns a non-NULL vma, it holds a reference to
+ * the task_struct, and holds read lock on vma->mm->mmap_lock.
+ * If this function returns NULL, it does not hold any reference or
+ * lock.
+ */
+again:
We can move label "again" to below right before "curr_task =
task_seq_get_next()" since "goto again" always having info->task == NULL.
+ if (info->task) {
+ curr_task = info->task;
+ curr_vma = info->vma;
+ /* In case of lock contention, drop mmap_lock to unblock
+ * the writer.
+ */
+ if (mmap_lock_is_contended(curr_task->mm)) {
+ info->prev_vm_start = curr_vma->vm_start;
+ info->prev_vm_end = curr_vma->vm_end;
+ op = task_vma_iter_find_vma;
+ mmap_read_unlock(curr_task->mm);
+ if (mmap_read_lock_killable(curr_task->mm))
Could you explain when mmap_read_lock_killable() may fail?
What I try to find is if mmap_read_lock_killable() fails, we should
abort iterating or we may request user to try again (if user buffer
is not filled anything).
+ goto finish;
+ } else {
+ op = task_vma_iter_next_vma;
+ }
+ } else {
+ curr_task = task_seq_get_next(ns, &curr_tid, true);
+ if (!curr_task) {
+ info->tid = curr_tid + 1;
+ goto finish;
+ }
+
+ if (curr_tid != info->tid) {
+ info->tid = curr_tid;
+ op = task_vma_iter_first_vma;
+ } else {
+ op = task_vma_iter_find_vma;
+ }
+
+ if (!curr_task->mm)
+ goto next_task;
+
+ if (mmap_read_lock_killable(curr_task->mm))
+ goto finish;
+ }
+
+ switch (op) {
+ case task_vma_iter_first_vma:
+ curr_vma = curr_task->mm->mmap;
+ break;
+ case task_vma_iter_next_vma:
+ curr_vma = curr_vma->vm_next;
+ break;
+ case task_vma_iter_find_vma:
+ /* We dropped mmap_lock so it is necessary to use find_vma
+ * to find the next vma. This is similar to the mechanism
+ * in show_smaps_rollup().
+ */
+ curr_vma = find_vma(curr_task->mm, info->prev_vm_end - 1);
+
+ if (curr_vma && (curr_vma->vm_start == info->prev_vm_start))
+ curr_vma = curr_vma->vm_next;
+ break;
+ }
+ if (!curr_vma) {
+ mmap_read_unlock(curr_task->mm);
+ goto next_task;
+ }
+ info->task = curr_task;
+ info->vma = curr_vma;
+ return curr_vma;
+
+next_task:
+ put_task_struct(curr_task);
+ info->task = NULL;
+ curr_tid++;
+ goto again;
+
+finish:
+ info->task = NULL;
+ info->vma = NULL;
+ return NULL;
+}
+
+static void *task_vma_seq_start(struct seq_file *seq, loff_t *pos)
+{
+ struct bpf_iter_seq_task_vma_info *info = seq->private;
+ struct vm_area_struct *vma;
+
+ vma = task_vma_seq_get_next(info);
+ if (vma && *pos == 0)
+ ++*pos;
+
+ return vma;
+}
+
+static void *task_vma_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+ struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+ ++*pos;
+ return task_vma_seq_get_next(info);
+}
+
+struct bpf_iter__task_vma {
+ __bpf_md_ptr(struct bpf_iter_meta *, meta);
+ __bpf_md_ptr(struct task_struct *, task);
+ __bpf_md_ptr(struct vm_area_struct *, vma);
+};
+
+DEFINE_BPF_ITER_FUNC(task_vma, struct bpf_iter_meta *meta,
+ struct task_struct *task, struct vm_area_struct *vma)
+
+static int __task_vma_seq_show(struct seq_file *seq, bool in_stop)
+{
+ struct bpf_iter_seq_task_vma_info *info = seq->private;
+ struct bpf_iter__task_vma ctx;
+ struct bpf_iter_meta meta;
+ struct bpf_prog *prog;
+
+ meta.seq = seq;
+ prog = bpf_iter_get_info(&meta, in_stop);
+ if (!prog)
+ return 0;
+
+ ctx.meta = &meta;
+ ctx.task = info->task;
+ ctx.vma = info->vma;
+ return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int task_vma_seq_show(struct seq_file *seq, void *v)
+{
+ return __task_vma_seq_show(seq, false);
+}
+
+static void task_vma_seq_stop(struct seq_file *seq, void *v)
+{
+ struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+ if (!v) {
+ (void)__task_vma_seq_show(seq, true);
+ } else {
+ info->prev_vm_start = info->vma->vm_start;
+ info->prev_vm_end = info->vma->vm_end;
This change, together with task_vma_iter_find_vma action,
is not correct.
What we typically have is info->vma->vm_start/info->vma->vm_end
is the next show but since there is no room for that we will
delay until user space processed buffer and come back.
So here, it is not prev_vm_start/end as it has not been
displayed.
Maybe you can separate task_vma_iter_find_vma into two?
task_vma_iter_find_vma and task_vma_iter_find_vma_next.
(task_vma_iter_find_vma_next carriers the action with
what you have now for task_vma_iter_find_vma).
In the above task_vma_seq_get_next(), if info->task != NULL,
you will use task_vma_iter_find_vma_next (the one after previous
vm_start/end), if info->task == NULL, which means back from user
space, not going to next vma if there is an exact match.
+ mmap_read_unlock(info->task->mm);
+ put_task_struct(info->task);
+ info->task = NULL;
+ }
+}
+
+static const struct seq_operations task_vma_seq_ops = {
+ .start = task_vma_seq_start,
+ .next = task_vma_seq_next,
+ .stop = task_vma_seq_stop,
+ .show = task_vma_seq_show,
+};
+
BTF_ID_LIST(btf_task_file_ids)
BTF_ID(struct, task_struct)
BTF_ID(struct, file)
+BTF_ID(struct, vm_area_struct)
static const struct bpf_iter_seq_info task_seq_info = {
.seq_ops = &task_seq_ops,
@@ -346,6 +529,26 @@ static struct bpf_iter_reg task_file_reg_info = {
.seq_info = &task_file_seq_info,
};
+static const struct bpf_iter_seq_info task_vma_seq_info = {
+ .seq_ops = &task_vma_seq_ops,
+ .init_seq_private = init_seq_pidns,
+ .fini_seq_private = fini_seq_pidns,
+ .seq_priv_size = sizeof(struct bpf_iter_seq_task_vma_info),
+};
+
+static struct bpf_iter_reg task_vma_reg_info = {
+ .target = "task_vma",
+ .feature = BPF_ITER_RESCHED,
+ .ctx_arg_info_size = 2,
+ .ctx_arg_info = {
+ { offsetof(struct bpf_iter__task_vma, task),
+ PTR_TO_BTF_ID_OR_NULL },
+ { offsetof(struct bpf_iter__task_vma, vma),
+ PTR_TO_BTF_ID_OR_NULL },
+ },
+ .seq_info = &task_vma_seq_info,
+};
+
static int __init task_iter_init(void)
{
int ret;
@@ -357,6 +560,12 @@ static int __init task_iter_init(void)
task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
- return bpf_iter_reg_target(&task_file_reg_info);
+ ret = bpf_iter_reg_target(&task_file_reg_info);
+ if (ret)
+ return ret;
+
+ task_vma_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
+ task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[2];
+ return bpf_iter_reg_target(&task_vma_reg_info);
}
late_initcall(task_iter_init);
