diff mbox series

[bpf-next,2/3] bpf: Free local storage memory after one RCU-tasks-trace grace period

Message ID 20221011071128.3470622-3-houtao@huaweicloud.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Remove unnecessary RCU grace period chaining | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 2 this patch: 2
netdev/cc_maintainers warning 2 maintainers not CCed: song@kernel.org martin.lau@linux.dev
netdev/build_clang success Errors and warnings before: 5 this patch: 5
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 2 this patch: 2
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 28 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-PR fail PR summary
bpf/vmtest-bpf-next-VM_Test-4 success Logs for llvm-toolchain
bpf/vmtest-bpf-next-VM_Test-5 success Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-2 success Logs for build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-3 success Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-1 success Logs for build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-7 success Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-8 success Logs for test_maps on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-10 fail Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-13 fail Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-14 fail Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-16 success Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-17 success Logs for test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-6 success Logs for test_maps on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-11 fail Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-9 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-15 success Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-12 success Logs for test_progs_no_alu32 on s390x with gcc

Commit Message

Hou Tao Oct. 11, 2022, 7:11 a.m. UTC 
From: Hou Tao <houtao1@huawei.com>

Local storage map is accessible for both sleepable and normal bpf
program, so its memory is freed by using both call_rcu_tasks_trace() and
kfree_rcu() to wait for both RCU-tasks-trace grace period and RCU grace
period to expire.

However According to the current implementation of RCU-tasks-trace, one
RCU-tasks-trace grace period waits for one RCU grace period, so there is
no need to call kfree_rcu(), it is safe to call kfree() directly.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 kernel/bpf/bpf_local_storage.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Comments

Paul E. McKenney Oct. 11, 2022, 9:09 a.m. UTC | #1 
On Tue, Oct 11, 2022 at 03:11:27PM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> Local storage map is accessible for both sleepable and normal bpf
> program, so its memory is freed by using both call_rcu_tasks_trace() and
> kfree_rcu() to wait for both RCU-tasks-trace grace period and RCU grace
> period to expire.
> 
> However According to the current implementation of RCU-tasks-trace, one
> RCU-tasks-trace grace period waits for one RCU grace period, so there is
> no need to call kfree_rcu(), it is safe to call kfree() directly.

Again, this is true, but this is an implementation detail that is not
guaranteed in future versions of the kernel.  But if this additional
call_rcu() is causing trouble, I could add some API member that
returned true in kernels where it does happen to be the case that
call_rcu_tasks_trace() implies a call_rcu()-style grace period.

The BPF local storage code could then complain or adapt, as appropriate.

Again, thoughts?

							Thanx, Paul

> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
>  kernel/bpf/bpf_local_storage.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> index 802fc15b0d73..18a2dd611635 100644
> --- a/kernel/bpf/bpf_local_storage.c
> +++ b/kernel/bpf/bpf_local_storage.c
> @@ -84,20 +84,26 @@ bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
>  	return NULL;
>  }
>  
> +/* Now RCU Tasks grace period implies RCU grace period, so no need to call
> + * kfree_rcu(), just call kfree() directly.
> + */
>  void bpf_local_storage_free_rcu(struct rcu_head *rcu)
>  {
>  	struct bpf_local_storage *local_storage;
>  
>  	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
> -	kfree_rcu(local_storage, rcu);
> +	kfree(local_storage);
>  }
>  
> +/* Now RCU Tasks grace period implies RCU grace period, so no need to call
> + * kfree_rcu(), just call kfree() directly.
> + */
>  static void bpf_selem_free_rcu(struct rcu_head *rcu)
>  {
>  	struct bpf_local_storage_elem *selem;
>  
>  	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
> -	kfree_rcu(selem, rcu);
> +	kfree(selem);
>  }
>  
>  /* local_storage->lock must be held and selem->local_storage == local_storage.
> -- 
> 2.29.2
>
diff mbox series

Patch

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 802fc15b0d73..18a2dd611635 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -84,20 +84,26 @@  bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
 	return NULL;
 }
 
+/* Now RCU Tasks grace period implies RCU grace period, so no need to call
+ * kfree_rcu(), just call kfree() directly.
+ */
 void bpf_local_storage_free_rcu(struct rcu_head *rcu)
 {
 	struct bpf_local_storage *local_storage;
 
 	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
-	kfree_rcu(local_storage, rcu);
+	kfree(local_storage);
 }
 
+/* Now RCU Tasks grace period implies RCU grace period, so no need to call
+ * kfree_rcu(), just call kfree() directly.
+ */
 static void bpf_selem_free_rcu(struct rcu_head *rcu)
 {
 	struct bpf_local_storage_elem *selem;
 
 	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
-	kfree_rcu(selem, rcu);
+	kfree(selem);
 }
 
 /* local_storage->lock must be held and selem->local_storage == local_storage.