| Message ID | 1606214969-97849-2-git-send-email-linyunsheng@huawei.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Add an assert in napi_consume_skb() | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for net-next |
| netdev/subject_prefix | success | Link |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 30851 this patch: 30851 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | warning | WARNING: Single statement macros should not use a do {} while (0) loop |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 29001 this patch: 29001 |
| netdev/header_inline | success | Link |
| netdev/stable | success | Stable not CCed |
On Tue, 24 Nov 2020 18:49:28 +0800 Yunsheng Lin wrote: > The current semantic for napi_consume_skb() is that caller need > to provide non-zero budget when calling from NAPI context, and > breaking this semantic will cause hard to debug problem, because > _kfree_skb_defer() need to run in atomic context in order to push > the skb to the particular cpu' napi_alloc_cache atomically. > > So add the lockdep_assert_in_softirq() to assert when the running > context is not in_softirq, in_softirq means softirq is serving or > BH is disabled, which has a ambiguous semantics due to the BH > disabled confusion, so add a comment to emphasize that. > > And the softirq context can be interrupted by hard IRQ or NMI > context, lockdep_assert_in_softirq() need to assert about hard > IRQ or NMI context too. > > Suggested-by: Jakub Kicinski <kuba@kernel.org> > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> > --- > V3: add comment to emphasize the ambiguous semantics. > --- > include/linux/lockdep.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > index f559487..8d60f46 100644 > --- a/include/linux/lockdep.h > +++ b/include/linux/lockdep.h > @@ -594,6 +594,13 @@ do { \ > this_cpu_read(hardirqs_enabled))); \ > } while (0) > > +/* Much like in_softirq() - semantics are ambiguous, use carefully. */ I've added both of the comments I suggested in the reply to Peter here and applied to net-next. Thanks for working on this. > +#define lockdep_assert_in_softirq() \ > +do { \ > + WARN_ON_ONCE(__lockdep_enabled && \ > + (!in_softirq() || in_irq() || in_nmi())); \ > +} while (0)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index f559487..8d60f46 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -594,6 +594,13 @@ do { \ this_cpu_read(hardirqs_enabled))); \ } while (0) +/* Much like in_softirq() - semantics are ambiguous, use carefully. */ +#define lockdep_assert_in_softirq() \ +do { \ + WARN_ON_ONCE(__lockdep_enabled && \ + (!in_softirq() || in_irq() || in_nmi())); \ +} while (0) + #else # define might_lock(lock) do { } while (0) # define might_lock_read(lock) do { } while (0) @@ -605,6 +612,7 @@ do { \ # define lockdep_assert_preemption_enabled() do { } while (0) # define lockdep_assert_preemption_disabled() do { } while (0) +# define lockdep_assert_in_softirq() do { } while (0) #endif #ifdef CONFIG_PROVE_RAW_LOCK_NESTING
The current semantic for napi_consume_skb() is that caller need to provide non-zero budget when calling from NAPI context, and breaking this semantic will cause hard to debug problem, because _kfree_skb_defer() need to run in atomic context in order to push the skb to the particular cpu' napi_alloc_cache atomically. So add the lockdep_assert_in_softirq() to assert when the running context is not in_softirq, in_softirq means softirq is serving or BH is disabled, which has a ambiguous semantics due to the BH disabled confusion, so add a comment to emphasize that. And the softirq context can be interrupted by hard IRQ or NMI context, lockdep_assert_in_softirq() need to assert about hard IRQ or NMI context too. Suggested-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> --- V3: add comment to emphasize the ambiguous semantics. --- include/linux/lockdep.h | 8 ++++++++ 1 file changed, 8 insertions(+)