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Merge branch 'transfer-rcu-lock-state-across-subprog-calls'

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Kumar Kartikeya Dwivedi says:

====================
Transfer RCU lock state across subprog calls

David suggested during the discussion in [0] that we should handle RCU
locks in a similar fashion to spin locks where the verifier understands
when a lock held in a caller is released in callee, or lock taken in
callee is released in a caller, or the callee is called within a lock
critical section. This set extends the same semantics to RCU read locks
and adds a few selftests to verify correct behavior. This issue has also
come up for sched-ext programs.

This would now allow static subprog calls to be made without errors
within RCU read sections, for subprogs to release RCU locks of callers
and return to them, or for subprogs to take RCU lock which is later
released in the caller.

  [0]: https://lore.kernel.org/bpf/20240204120206.796412-1-memxor@gmail.com

Changelog:
----------
v1 -> v2:
v1: https://lore.kernel.org/bpf/20240204230231.1013964-1-memxor@gmail.com

 * Add tests for global subprog behaviour (Yafang)
 * Add Acks, Tested-by (Yonghong, Yafang)
====================

Link: https://lore.kernel.org/r/20240205055646.1112186-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2024-02-05 20:00:14 -08:00
commit 20a286c1a3
3 changed files with 127 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
kernel/bpf/verifier.c
View file

@ -17703,8 +17703,7 @@ static int do_check(struct bpf_verifier_env *env)
return -EINVAL;
}
if (env->cur_state->active_rcu_lock &&
!in_rbtree_lock_required_cb(env)) {
if (env->cur_state->active_rcu_lock && !env->cur_state->curframe) {
verbose(env, "bpf_rcu_read_unlock is missing\n");
return -EINVAL;
}

6
tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c
View file

@ -29,6 +29,10 @@ static void test_success(void)
bpf_program__set_autoload(skel->progs.non_sleepable_1, true);
bpf_program__set_autoload(skel->progs.non_sleepable_2, true);
bpf_program__set_autoload(skel->progs.task_trusted_non_rcuptr, true);
bpf_program__set_autoload(skel->progs.rcu_read_lock_subprog, true);
bpf_program__set_autoload(skel->progs.rcu_read_lock_global_subprog, true);
bpf_program__set_autoload(skel->progs.rcu_read_lock_subprog_lock, true);
bpf_program__set_autoload(skel->progs.rcu_read_lock_subprog_unlock, true);
err = rcu_read_lock__load(skel);
if (!ASSERT_OK(err, "skel_load"))
goto out;
@ -75,6 +79,8 @@ static const char * const inproper_region_tests[] = {
"inproper_sleepable_helper",
"inproper_sleepable_kfunc",
"nested_rcu_region",
"rcu_read_lock_global_subprog_lock",
"rcu_read_lock_global_subprog_unlock",
};
static void test_inproper_region(void)

120
tools/testing/selftests/bpf/progs/rcu_read_lock.c
View file

@ -319,3 +319,123 @@ int cross_rcu_region(void *ctx)
bpf_rcu_read_unlock();
return 0;
}
__noinline
static int static_subprog(void *ctx)
{
volatile int ret = 0;
if (bpf_get_prandom_u32())
return ret + 42;
return ret + bpf_get_prandom_u32();
}
__noinline
int global_subprog(u64 a)
{
volatile int ret = a;
return ret + static_subprog(NULL);
}
__noinline
static int static_subprog_lock(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_lock();
if (bpf_get_prandom_u32())
return ret + 42;
return ret + bpf_get_prandom_u32();
}
__noinline
int global_subprog_lock(u64 a)
{
volatile int ret = a;
return ret + static_subprog_lock(NULL);
}
__noinline
static int static_subprog_unlock(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_unlock();
if (bpf_get_prandom_u32())
return ret + 42;
return ret + bpf_get_prandom_u32();
}
__noinline
int global_subprog_unlock(u64 a)
{
volatile int ret = a;
return ret + static_subprog_unlock(NULL);
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_subprog(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_lock();
if (bpf_get_prandom_u32())
ret += static_subprog(ctx);
bpf_rcu_read_unlock();
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_global_subprog(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_lock();
if (bpf_get_prandom_u32())
ret += global_subprog(ret);
bpf_rcu_read_unlock();
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_subprog_lock(void *ctx)
{
volatile int ret = 0;
ret += static_subprog_lock(ctx);
bpf_rcu_read_unlock();
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_global_subprog_lock(void *ctx)
{
volatile int ret = 0;
ret += global_subprog_lock(ret);
bpf_rcu_read_unlock();
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_subprog_unlock(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_lock();
ret += static_subprog_unlock(ctx);
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
int rcu_read_lock_global_subprog_unlock(void *ctx)
{
volatile int ret = 0;
bpf_rcu_read_lock();
ret += global_subprog_unlock(ret);
return 0;
}