Re: [PATCH bpf-next v4 1/3] bpf: Add map tracing functions and call sites

From: Joe Burton <redacted>

Add two functions that fentry/fexit/fmod_ret programs can attach to:
	bpf_map_trace_update_elem
	bpf_map_trace_delete_elem
These functions have the same arguments as bpf_map_{update,delete}_elem.

Invoke these functions from the following map types:
	BPF_MAP_TYPE_ARRAY
	BPF_MAP_TYPE_PERCPU_ARRAY
	BPF_MAP_TYPE_HASH
	BPF_MAP_TYPE_PERCPU_HASH
	BPF_MAP_TYPE_LRU_HASH
	BPF_MAP_TYPE_LRU_PERCPU_HASH

The only guarantee about these functions is that they are invoked before
the corresponding action occurs. Other conditions may prevent the
corresponding action from occurring after the function is invoked.

Signed-off-by: Joe Burton <redacted>
---
  kernel/bpf/Makefile    |  2 +-
  kernel/bpf/arraymap.c  |  4 +++-
  kernel/bpf/hashtab.c   | 20 +++++++++++++++++++-
  kernel/bpf/map_trace.c | 17 +++++++++++++++++
  kernel/bpf/map_trace.h | 19 +++++++++++++++++++
  5 files changed, 59 insertions(+), 3 deletions(-)
  create mode 100644 kernel/bpf/map_trace.c
  create mode 100644 kernel/bpf/map_trace.h

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index c1a9be6a4b9f..0cf38dab339a 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile

@@ -9,7 +9,7 @@ CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy)
  obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o
  obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
  obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o
-obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
+obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o map_trace.o
  obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
  obj-$(CONFIG_BPF_SYSCALL) += disasm.o
  obj-$(CONFIG_BPF_JIT) += trampoline.o

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index c7a5be3bf8be..e9e7bd27ffad 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c

@@ -13,6 +13,7 @@
  #include <linux/rcupdate_trace.h>
  
  #include "map_in_map.h"
+#include "map_trace.h"
  
  #define ARRAY_CREATE_FLAG_MASK \
  	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK | \

@@ -329,7 +330,8 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
  			copy_map_value(map, val, value);
  		check_and_free_timer_in_array(array, val);
  	}
-	return 0;
+
+	return bpf_map_trace_update_elem(map, key, value, map_flags);

@@ -1133,6 +1137,10 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
  		/* unknown flags */
  		return -EINVAL;
  
+	ret = bpf_map_trace_update_elem(map, key, value, map_flags);
+	if (unlikely(ret))
+		return ret;
+
  	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
  		     !rcu_read_lock_bh_held());
  

@@ -1182,6 +1190,8 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
  	else if (l_old)
  		htab_lru_push_free(htab, l_old);
  
+	if (!ret)
+		ret = bpf_map_trace_update_elem(map, key, value, map_flags);
  	return ret;
  }