* [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket
@ 2023-10-05 3:23 Song Liu
2023-10-05 6:31 ` Song Liu
0 siblings, 1 reply; 4+ messages in thread
From: Song Liu @ 2023-10-05 3:23 UTC (permalink / raw)
To: bpf; +Cc: ast, daniel, andrii, martin.lau, kernel-team, Song Liu, Tejun Heo
htab_lock_bucket uses the following logic to avoid recursion:
1. preempt_disable();
2. check percpu counter htab->map_locked[hash] for recursion;
2.1. if map_lock[hash] is already taken, return -BUSY;
3. raw_spin_lock_irqsave();
However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ
logic will not able to access the same hash of the hashtab and get -EBUSY.
This -EBUSY is not really necessary. Fix it by disabling IRQ before
checking map_locked:
1. preempt_disable();
2. local_irq_save();
3. check percpu counter htab->map_locked[hash] for recursion;
3.1. if map_lock[hash] is already taken, return -BUSY;
4. raw_spin_lock().
Similarly, use raw_spin_unlock() and local_irq_restore() in
htab_unlock_bucket().
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Song Liu <song@kernel.org>
---
Changes in v3:
1. Use raw_local_irq_* APIs instead.
Changes in v2:
1. Use raw_spin_unlock() and local_irq_restore() in htab_unlock_bucket().
(Andrii)
---
kernel/bpf/hashtab.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index a8c7e1c5abfa..74c8d1b41dd5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -155,13 +155,15 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab,
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
preempt_disable();
+ raw_local_irq_save(flags);
if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
__this_cpu_dec(*(htab->map_locked[hash]));
+ raw_local_irq_restore(flags);
preempt_enable();
return -EBUSY;
}
- raw_spin_lock_irqsave(&b->raw_lock, flags);
+ raw_spin_lock(&b->raw_lock);
*pflags = flags;
return 0;
@@ -172,8 +174,9 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab,
unsigned long flags)
{
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
- raw_spin_unlock_irqrestore(&b->raw_lock, flags);
+ raw_spin_unlock(&b->raw_lock);
__this_cpu_dec(*(htab->map_locked[hash]));
+ raw_local_irq_restore(flags);
preempt_enable();
}
--
2.34.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket
2023-10-05 3:23 [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket Song Liu
@ 2023-10-05 6:31 ` Song Liu
0 siblings, 0 replies; 4+ messages in thread
From: Song Liu @ 2023-10-05 6:31 UTC (permalink / raw)
To: Song Liu
Cc: bpf, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Kernel Team, Tejun Heo
> On Oct 4, 2023, at 8:23 PM, Song Liu <song@kernel.org> wrote:
>
> htab_lock_bucket uses the following logic to avoid recursion:
>
> 1. preempt_disable();
> 2. check percpu counter htab->map_locked[hash] for recursion;
> 2.1. if map_lock[hash] is already taken, return -BUSY;
> 3. raw_spin_lock_irqsave();
>
> However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ
> logic will not able to access the same hash of the hashtab and get -EBUSY.
> This -EBUSY is not really necessary. Fix it by disabling IRQ before
> checking map_locked:
>
> 1. preempt_disable();
> 2. local_irq_save();
> 3. check percpu counter htab->map_locked[hash] for recursion;
> 3.1. if map_lock[hash] is already taken, return -BUSY;
> 4. raw_spin_lock().
>
> Similarly, use raw_spin_unlock() and local_irq_restore() in
> htab_unlock_bucket().
>
> Suggested-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Song Liu <song@kernel.org>
Somehow this didn't make to lore and thus not to patchwork. Let
me resend, sorry for the noise.
Song
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket
2023-10-05 6:31 Song Liu
@ 2023-10-05 17:52 ` Song Liu
0 siblings, 0 replies; 4+ messages in thread
From: Song Liu @ 2023-10-05 17:52 UTC (permalink / raw)
To: bpf; +Cc: ast, daniel, andrii, martin.lau, kernel-team, Tejun Heo
On Wed, Oct 4, 2023 at 11:32 PM Song Liu <song@kernel.org> wrote:
>
> htab_lock_bucket uses the following logic to avoid recursion:
>
> 1. preempt_disable();
> 2. check percpu counter htab->map_locked[hash] for recursion;
> 2.1. if map_lock[hash] is already taken, return -BUSY;
> 3. raw_spin_lock_irqsave();
>
> However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ
> logic will not able to access the same hash of the hashtab and get -EBUSY.
> This -EBUSY is not really necessary. Fix it by disabling IRQ before
> checking map_locked:
>
> 1. preempt_disable();
> 2. local_irq_save();
> 3. check percpu counter htab->map_locked[hash] for recursion;
> 3.1. if map_lock[hash] is already taken, return -BUSY;
> 4. raw_spin_lock().
>
> Similarly, use raw_spin_unlock() and local_irq_restore() in
> htab_unlock_bucket().
>
> Suggested-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Song Liu <song@kernel.org>
This still doesn't look right. Let me try more..
Thanks,
Song
>
> ---
> Changes in v3:
> 1. Use raw_local_irq_* APIs instead.
>
> Changes in v2:
> 1. Use raw_spin_unlock() and local_irq_restore() in htab_unlock_bucket().
> (Andrii)
> ---
> kernel/bpf/hashtab.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index a8c7e1c5abfa..74c8d1b41dd5 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -155,13 +155,15 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab,
> hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
>
> preempt_disable();
> + raw_local_irq_save(flags);
> if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
> __this_cpu_dec(*(htab->map_locked[hash]));
> + raw_local_irq_restore(flags);
> preempt_enable();
> return -EBUSY;
> }
>
> - raw_spin_lock_irqsave(&b->raw_lock, flags);
> + raw_spin_lock(&b->raw_lock);
> *pflags = flags;
>
> return 0;
> @@ -172,8 +174,9 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab,
> unsigned long flags)
> {
> hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
> - raw_spin_unlock_irqrestore(&b->raw_lock, flags);
> + raw_spin_unlock(&b->raw_lock);
> __this_cpu_dec(*(htab->map_locked[hash]));
> + raw_local_irq_restore(flags);
> preempt_enable();
> }
>
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket
@ 2023-10-05 6:31 Song Liu
2023-10-05 17:52 ` Song Liu
0 siblings, 1 reply; 4+ messages in thread
From: Song Liu @ 2023-10-05 6:31 UTC (permalink / raw)
To: bpf; +Cc: ast, daniel, andrii, martin.lau, kernel-team, Song Liu, Tejun Heo
htab_lock_bucket uses the following logic to avoid recursion:
1. preempt_disable();
2. check percpu counter htab->map_locked[hash] for recursion;
2.1. if map_lock[hash] is already taken, return -BUSY;
3. raw_spin_lock_irqsave();
However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ
logic will not able to access the same hash of the hashtab and get -EBUSY.
This -EBUSY is not really necessary. Fix it by disabling IRQ before
checking map_locked:
1. preempt_disable();
2. local_irq_save();
3. check percpu counter htab->map_locked[hash] for recursion;
3.1. if map_lock[hash] is already taken, return -BUSY;
4. raw_spin_lock().
Similarly, use raw_spin_unlock() and local_irq_restore() in
htab_unlock_bucket().
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Song Liu <song@kernel.org>
---
Changes in v3:
1. Use raw_local_irq_* APIs instead.
Changes in v2:
1. Use raw_spin_unlock() and local_irq_restore() in htab_unlock_bucket().
(Andrii)
---
kernel/bpf/hashtab.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index a8c7e1c5abfa..74c8d1b41dd5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -155,13 +155,15 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab,
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
preempt_disable();
+ raw_local_irq_save(flags);
if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
__this_cpu_dec(*(htab->map_locked[hash]));
+ raw_local_irq_restore(flags);
preempt_enable();
return -EBUSY;
}
- raw_spin_lock_irqsave(&b->raw_lock, flags);
+ raw_spin_lock(&b->raw_lock);
*pflags = flags;
return 0;
@@ -172,8 +174,9 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab,
unsigned long flags)
{
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
- raw_spin_unlock_irqrestore(&b->raw_lock, flags);
+ raw_spin_unlock(&b->raw_lock);
__this_cpu_dec(*(htab->map_locked[hash]));
+ raw_local_irq_restore(flags);
preempt_enable();
}
--
2.34.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
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