Messages in this thread | | | From | Dragos Tatulea <> | Subject | Re: [RFC PATCH] net: Fix one page_pool page leak from skb_frag_unref | Date | Thu, 25 Apr 2024 19:47:55 +0000 |
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On Thu, 2024-04-25 at 12:20 -0700, Mina Almasry wrote: > On Thu, Apr 25, 2024 at 1:17 AM Dragos Tatulea <dtatulea@nvidia.com> wrote: > > > > On Wed, 2024-04-24 at 15:08 -0700, Mina Almasry wrote: > > > If that doesn't work, I think I prefer > > > reverting a580ea994fd3 ("net: mirror skb frag ref/unref helpers") > > > rather than merging this fix to make sure we removed the underlying > > > cause of the issue. > > This is the safest bet. > > > > So, to recap, I see 2 possibilities: > > > > 1) Revert a580ea994fd3 ("net: mirror skb frag ref/unref helpers"): safe, but it > > will probably have to come back in one way or another. > > 2) Drop the recycle checks from skb_frag_ref/unref: this enforces the rule of > > always referencing/dereferencing pages based on their type (page_pool or > > normal). > > > > If this works, I would be very happy. I personally think ref/unref > should be done based on the page type. For me the net stack using the > regular {get|put}_page on a pp page isn't great. It requires special > handling to make sure the ref + unref are in sync. Also if the last pp > ref is dropped while there are pending regular refs, > __page_pool_page_can_be_recycled() check will fail and the page will > not be recycled. > > On the other hand, since 0a149ab78ee2 ("page_pool: transition to > reference count management after page draining") I'm not sure there is > any reason to continue to use get/put_page on pp-pages, we can use the > new pp-ref instead. > > I don't see any regressions with this diff (needs cleanup), but your > test setup seems much much better than mine (I think this is the > second reffing issue you manage to repro): > > diff --git a/include/linux/skbuff_ref.h b/include/linux/skbuff_ref.h > index 4dcdbe9fbc5f..4c72227dce1b 100644 > --- a/include/linux/skbuff_ref.h > +++ b/include/linux/skbuff_ref.h > @@ -31,7 +31,7 @@ static inline bool napi_pp_get_page(struct page *page) > static inline void skb_page_ref(struct page *page, bool recycle) > { > #ifdef CONFIG_PAGE_POOL > - if (recycle && napi_pp_get_page(page)) > + if (napi_pp_get_page(page)) > return; > #endif > get_page(page); > @@ -69,7 +69,7 @@ static inline void > skb_page_unref(struct page *page, bool recycle) > { > #ifdef CONFIG_PAGE_POOL > - if (recycle && napi_pp_put_page(page)) > + if (napi_pp_put_page(page)) > return; > #endif > put_page(page); > > This is option 2. I thought this would fix everything. But I just tested and it's not the case: we are now reaching a negative pp_ref_count. So probably somewhere a regular page reference is still being taken...
Thanks, Dragos
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