On Thu, Mar 12, 2026 at 2:48 PM Michael S. Tsirkin <[email protected]> wrote: > > On Thu, Mar 12, 2026 at 02:17:16PM +0100, Eric Dumazet wrote: > > On Thu, Mar 12, 2026 at 2:06 PM Simon Schippers > > <[email protected]> wrote: > > > > > > This patch moves the check for available free space for a new entry into > > > a separate function. As a result, __ptr_ring_produce() remains logically > > > unchanged, while the new helper allows callers to determine in advance > > > whether subsequent __ptr_ring_produce() calls will succeed. This > > > information can, for example, be used to temporarily stop producing until > > > __ptr_ring_peek() indicates that space is available again. > > > > > > Co-developed-by: Tim Gebauer <[email protected]> > > > Signed-off-by: Tim Gebauer <[email protected]> > > > Signed-off-by: Simon Schippers <[email protected]> > > > --- > > > include/linux/ptr_ring.h | 14 ++++++++++++-- > > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h > > > index 534531807d95..a5a3fa4916d3 100644 > > > --- a/include/linux/ptr_ring.h > > > +++ b/include/linux/ptr_ring.h > > > @@ -96,6 +96,14 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r) > > > return ret; > > > } > > > > > > +static inline int __ptr_ring_produce_peek(struct ptr_ring *r) > > > +{ > > > + if (unlikely(!r->size) || r->queue[r->producer]) > > > > I think this should be > > > > if (unlikely(!r->size) || READ_ONCE(r->queue[r->producer])) > > > > And of course: > > > > @@ -194,7 +194,7 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r) > > static inline bool __ptr_ring_empty(struct ptr_ring *r) > > { > > if (likely(r->size)) > > - return !r->queue[READ_ONCE(r->consumer_head)]; > > + return !READ_ONCE(r->queue[READ_ONCE(r->consumer_head)]); > > return true; > > } > > > I don't understand why it's necessary. consumer_head etc are > all lock protected. > > queue itself is not but we are only checking it for NULL - > it is fine if compiler reads it in many chunks and not all > at once. > > > @@ -256,7 +256,7 @@ static inline void __ptr_ring_zero_tail(struct > > ptr_ring *r, int consumer_head) > > * besides the first one until we write out all entries. > > */ > > while (likely(head > r->consumer_tail)) > > - r->queue[--head] = NULL; > > + WRITE_ONCE(r->queue[--head], NULL); > > > > r->consumer_tail = consumer_head; > > } > > > > > > Presumably we should fix this in net tree first. > > > Maybe this one yes but I am not sure at all - KCSAN is happy. >
Hmmm.. what about this trace ? BUG: KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue write to 0xffff88811d5ccc00 of 8 bytes by interrupt on cpu 0: __ptr_ring_zero_tail include/linux/ptr_ring.h:259 [inline] __ptr_ring_discard_one include/linux/ptr_ring.h:291 [inline] __ptr_ring_consume include/linux/ptr_ring.h:311 [inline] __skb_array_consume include/linux/skb_array.h:98 [inline] pfifo_fast_dequeue+0x770/0x8f0 net/sched/sch_generic.c:770 dequeue_skb net/sched/sch_generic.c:297 [inline] qdisc_restart net/sched/sch_generic.c:402 [inline] __qdisc_run+0x189/0xc80 net/sched/sch_generic.c:420 qdisc_run include/net/pkt_sched.h:120 [inline] net_tx_action+0x379/0x590 net/core/dev.c:5793 handle_softirqs+0xb9/0x280 kernel/softirq.c:622 do_softirq+0x45/0x60 kernel/softirq.c:523 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450 local_bh_enable include/linux/bottom_half.h:33 [inline] bpf_test_run+0x2db/0x620 net/bpf/test_run.c:426 bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline] __se_sys_bpf kernel/bpf/syscall.c:6339 [inline] __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff88811d5ccc00 of 8 bytes by task 22632 on cpu 1: __ptr_ring_produce include/linux/ptr_ring.h:106 [inline] ptr_ring_produce include/linux/ptr_ring.h:129 [inline] skb_array_produce include/linux/skb_array.h:44 [inline] pfifo_fast_enqueue+0xd5/0x2c0 net/sched/sch_generic.c:741 dev_qdisc_enqueue net/core/dev.c:4144 [inline] __dev_xmit_skb net/core/dev.c:4188 [inline] __dev_queue_xmit+0x6a4/0x1f20 net/core/dev.c:4795 dev_queue_xmit include/linux/netdevice.h:3384 [inline] __bpf_tx_skb net/core/filter.c:2153 [inline] __bpf_redirect_common net/core/filter.c:2197 [inline] __bpf_redirect+0x862/0x990 net/core/filter.c:2204 ____bpf_clone_redirect net/core/filter.c:2487 [inline] bpf_clone_redirect+0x20c/0x290 net/core/filter.c:2450 bpf_prog_53f18857bc887b09+0x22/0x2a bpf_dispatcher_nop_func include/linux/bpf.h:1402 [inline] __bpf_prog_run include/linux/filter.h:723 [inline] bpf_prog_run include/linux/filter.h:730 [inline] bpf_test_run+0x29d/0x620 net/bpf/test_run.c:423 bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline] __se_sys_bpf kernel/bpf/syscall.c:6339 [inline] __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0xffff888104a93a00 -> 0x0000000000000000 Reported by Kernel Concurrency Sanitizer on: CPU: 1 UID: 0 PID: 22632 Comm: syz.0.4135 Tainted: G W syzkaller #0 PREEMPT(full) Tainted: [W]=WARN Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
