diff mbox series

[2/3] bpf: bpf_iter_task_next: use __next_thread() rather than next_thread()

Message ID 20231114163237.GA897@redhat.com (mailing list archive)
State Accepted
Commit 5a34f9dabd9aa567e2d37e1aa27a67f80acfaa1c
Delegated to: BPF
Headers show
Series bpf: kernel/bpf/task_iter.c: don't abuse next_thread() | expand

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bpf/vmtest-bpf-next-PR success PR summary
netdev/series_format warning Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1145 this patch: 1145
netdev/cc_maintainers warning 8 maintainers not CCed: haoluo@google.com song@kernel.org kpsingh@kernel.org jolsa@kernel.org john.fastabend@gmail.com martin.lau@linux.dev andrii@kernel.org sdf@google.com
netdev/build_clang success Errors and warnings before: 1162 this patch: 1162
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
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netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1172 this patch: 1172
netdev/checkpatch warning CHECK: braces {} should be used on all arms of this statement
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Commit Message

Oleg Nesterov Nov. 14, 2023, 4:32 p.m. UTC 
Lockless use of next_thread() should be avoided, kernel/bpf/task_iter.c
is the last user and the usage is wrong.

bpf_iter_task_next() can loop forever, "kit->pos == kit->task" can never
happen if kit->pos execs. Change this code to use __next_thread().

With or without this change the usage of kit->pos/task and next_task()
doesn't look nice, see the next patch.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/bpf/task_iter.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Comments

Yonghong Song Nov. 16, 2023, 3:34 a.m. UTC | #1 
On 11/14/23 11:32 AM, Oleg Nesterov wrote:
> Lockless use of next_thread() should be avoided, kernel/bpf/task_iter.c
> is the last user and the usage is wrong.
>
> bpf_iter_task_next() can loop forever, "kit->pos == kit->task" can never
> happen if kit->pos execs. Change this code to use __next_thread().
>
> With or without this change the usage of kit->pos/task and next_task()
> doesn't look nice, see the next patch.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>
diff mbox series

Patch

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 51ae15e2b290..d42e08d0d0b7 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -1015,12 +1015,11 @@  __bpf_kfunc struct task_struct *bpf_iter_task_next(struct bpf_iter_task *it)
 	if (flags == BPF_TASK_ITER_ALL_PROCS)
 		goto get_next_task;
 
-	kit->pos = next_thread(kit->pos);
-	if (kit->pos == kit->task) {
-		if (flags == BPF_TASK_ITER_PROC_THREADS) {
-			kit->pos = NULL;
+	kit->pos = __next_thread(kit->pos);
+	if (!kit->pos) {
+		if (flags == BPF_TASK_ITER_PROC_THREADS)
 			return pos;
-		}
+		kit->pos = kit->task;
 	} else
 		return pos;