Merge branch 'bpf_get_task_stack'

Song Liu says:

====================
This set introduces a new helper bpf_get_task_stack(). The primary use case
is to dump all /proc/*/stack to seq_file via bpf_iter__task.

A few different approaches have been explored and compared:

  1. A simple wrapper around stack_trace_save_tsk(), as v1 [1].

     This approach introduces new syntax, which is different to existing
     helper bpf_get_stack(). Therefore, this is not ideal.

  2. Extend get_perf_callchain() to support "task" as argument.

     This approach reuses most of bpf_get_stack(). However, extending
     get_perf_callchain() requires non-trivial changes to architecture
     specific code. Which is error prone.

  3. Current (v2) approach, leverages most of existing bpf_get_stack(), and
     uses stack_trace_save_tsk() to handle architecture specific logic.

[1] https://lore.kernel.org/netdev/20200623070802.2310018-1-songliubraving@fb.com/

Changes v4 => v5:
1. Rebase and work around git-am issue. (Alexei)
2. Update commit log for 4/4. (Yonghong)

Changes v3 => v4:
1. Simplify the selftests with bpf_iter.h. (Yonghong)
2. Add example output to commit log of 4/4. (Yonghong)

Changes v2 => v3:
1. Rebase on top of bpf-next. (Yonghong)
2. Sanitize get_callchain_entry(). (Peter)
3. Use has_callchain_buf for bpf_get_task_stack. (Andrii)
4. Other small clean up. (Yonghong, Andrii).

Changes v1 => v2:
1. Reuse most of bpf_get_stack() logic. (Andrii)
2. Fix unsigned long vs. u64 mismatch for 32-bit systems. (Yonghong)
3. Add %pB support in bpf_trace_printk(). (Daniel)
4. Fix buffer size to bytes.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 36 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0cb8ec948816..da9bf35a26f8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3285,6 +3285,39 @@ union bpf_attr {
  *		Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
  *	Return
  *		*sk* if casting is valid, or NULL otherwise.
+ *
+ * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
+ *	Description
+ *		Return a user or a kernel stack in bpf program provided buffer.
+ *		To achieve this, the helper needs *task*, which is a valid
+ *		pointer to struct task_struct. To store the stacktrace, the
+ *		bpf program provides *buf* with	a nonnegative *size*.
+ *
+ *		The last argument, *flags*, holds the number of stack frames to
+ *		skip (from 0 to 255), masked with
+ *		**BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ *		the following flags:
+ *
+ *		**BPF_F_USER_STACK**
+ *			Collect a user space stack instead of a kernel stack.
+ *		**BPF_F_USER_BUILD_ID**
+ *			Collect buildid+offset instead of ips for user stack,
+ *			only valid if **BPF_F_USER_STACK** is also specified.
+ *
+ *		**bpf_get_task_stack**\ () can collect up to
+ *		**PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
+ *		to sufficient large buffer size. Note that
+ *		this limit can be controlled with the **sysctl** program, and
+ *		that it should be manually increased in order to profile long
+ *		user stacks (such as stacks for Java programs). To do so, use:
+ *
+ *		::
+ *
+ *			# sysctl kernel.perf_event_max_stack=<new value>
+ *	Return
+ *		A non-negative value equal to or less than *size* on success,
+ *		or a negative error in case of failure.
+ *
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3427,7 +3460,9 @@ union bpf_attr {
 	FN(skc_to_tcp_sock),		\
 	FN(skc_to_tcp_timewait_sock),	\
 	FN(skc_to_tcp_request_sock),	\
-	FN(skc_to_udp6_sock),
+	FN(skc_to_udp6_sock),		\
+	FN(get_task_stack),		\
+	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call