| Message ID | 20231012055741.3375999-1-song@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | a307f5a24924b5f0c45d003aefcb3327f3ed19aa |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket | expand |
Hello: This patch was applied to bpf/bpf.git (master) by Andrii Nakryiko <andrii@kernel.org>: On Wed, 11 Oct 2023 22:57:41 -0700 you 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(); > > [...] Here is the summary with links: - [bpf] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket https://git.kernel.org/bpf/bpf/c/a307f5a24924 You are awesome, thank you!
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index a8c7e1c5abfa..fd8d4b0addfc 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(); + local_irq_save(flags); if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) { __this_cpu_dec(*(htab->map_locked[hash])); + 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])); + local_irq_restore(flags); preempt_enable(); }
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> --- Resend to bpf tree to run CI with Ilya's s390 fixes. --- kernel/bpf/hashtab.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)