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Date: Fri, 08 Nov 2019 19:20:22 +0100
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: unlisted-recipients:; (no To-header on input)
Cc: Toke Høiland-Jørgensen <toke@...hat.com>,
netdev@...r.kernel.org,
Ilias Apalodimas <ilias.apalodimas@...aro.org>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Saeed Mahameed <saeedm@...lanox.com>,
Matteo Croce <mcroce@...hat.com>,
Jonathan Lemon <jonathan.lemon@...il.com>,
Lorenzo Bianconi <lorenzo@...nel.org>,
Tariq Toukan <tariqt@...lanox.com>
Subject: [net-next v1 PATCH 1/2] xdp: revert forced mem allocator removal
for page_pool
Forced removal of XDP mem allocator, specifically related to page_pool, turned
out to be a wrong approach. Special thanks to Jonathan Lemon for convincing me.
This patch is a partial revert of commit d956a048cd3f (“xdp: force mem allocator
removal and periodic warning”).
It is much better to provide a guarantee that page_pool object stays valid
until 'inflight' pages reach zero, making it safe to remove.
We keep the periodic warning via a work-queue, but increased interval to
5-minutes. The reason is to have a way to catch bugs, where inflight
pages/packets never reach zero, indicating some kind of leak. These kind of
bugs have been observed while converting drivers over to use page_pool API.
Details on when to crash the kernel. If page_pool API is misused and
somehow __page_pool_free() is invoked while there are still inflight
frames, then (like before) a WARN() is triggered and not a BUG(). This can
potentially lead to use-after-free, which we try to catch via poisoning the
page_pool object memory with some NULL pointers. Doing it this way,
pinpoint both the driver (likely) prematurely freeing page_pool via WARN(),
and crash-dump for inflight page/packet show who to blame for late return.
Fixes: d956a048cd3f (“xdp: force mem allocator removal and periodic warning”)
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
include/trace/events/xdp.h | 35 +++--------------------------------
net/core/page_pool.c | 8 ++++++--
net/core/xdp.c | 36 +++++++++++++-----------------------
3 files changed, 22 insertions(+), 57 deletions(-)
diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index c7e3c9c5bad3..a3ead2b1f00e 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -318,9 +318,9 @@ __MEM_TYPE_MAP(__MEM_TYPE_TP_FN)
TRACE_EVENT(mem_disconnect,
TP_PROTO(const struct xdp_mem_allocator *xa,
- bool safe_to_remove, bool force),
+ bool safe_to_remove),
- TP_ARGS(xa, safe_to_remove, force),
+ TP_ARGS(xa, safe_to_remove),
TP_STRUCT__entry(
__field(const struct xdp_mem_allocator *, xa)
@@ -328,7 +328,6 @@ TRACE_EVENT(mem_disconnect,
__field(u32, mem_type)
__field(const void *, allocator)
__field(bool, safe_to_remove)
- __field(bool, force)
__field(int, disconnect_cnt)
),
@@ -338,17 +337,15 @@ TRACE_EVENT(mem_disconnect,
__entry->mem_type = xa->mem.type;
__entry->allocator = xa->allocator;
__entry->safe_to_remove = safe_to_remove;
- __entry->force = force;
__entry->disconnect_cnt = xa->disconnect_cnt;
),
TP_printk("mem_id=%d mem_type=%s allocator=%p"
- " safe_to_remove=%s force=%s disconnect_cnt=%d",
+ " safe_to_remove=%s disconnect_cnt=%d",
__entry->mem_id,
__print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
__entry->allocator,
__entry->safe_to_remove ? "true" : "false",
- __entry->force ? "true" : "false",
__entry->disconnect_cnt
)
);
@@ -387,32 +384,6 @@ TRACE_EVENT(mem_connect,
)
);
-TRACE_EVENT(mem_return_failed,
-
- TP_PROTO(const struct xdp_mem_info *mem,
- const struct page *page),
-
- TP_ARGS(mem, page),
-
- TP_STRUCT__entry(
- __field(const struct page *, page)
- __field(u32, mem_id)
- __field(u32, mem_type)
- ),
-
- TP_fast_assign(
- __entry->page = page;
- __entry->mem_id = mem->id;
- __entry->mem_type = mem->type;
- ),
-
- TP_printk("mem_id=%d mem_type=%s page=%p",
- __entry->mem_id,
- __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
- __entry->page
- )
-);
-
#endif /* _TRACE_XDP_H */
#include <trace/define_trace.h>
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 5bc65587f1c4..226f2eb30418 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -346,7 +346,7 @@ static void __warn_in_flight(struct page_pool *pool)
distance = _distance(hold_cnt, release_cnt);
- /* Drivers should fix this, but only problematic when DMA is used */
+ /* BUG but warn as kernel should crash later */
WARN(1, "Still in-flight pages:%d hold:%u released:%u",
distance, hold_cnt, release_cnt);
}
@@ -360,12 +360,16 @@ void __page_pool_free(struct page_pool *pool)
WARN(pool->alloc.count, "API usage violation");
WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
- /* Can happen due to forced shutdown */
if (!__page_pool_safe_to_destroy(pool))
__warn_in_flight(pool);
ptr_ring_cleanup(&pool->ring, NULL);
+ /* Make sure kernel will crash on use-after-free */
+ pool->ring.queue = NULL;
+ pool->alloc.cache[PP_ALLOC_CACHE_SIZE - 1] = NULL;
+ pool->alloc.count = PP_ALLOC_CACHE_SIZE;
+
if (pool->p.flags & PP_FLAG_DMA_MAP)
put_device(pool->p.dev);
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 20781ad5f9c3..8673f199d9f4 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -85,7 +85,7 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
kfree(xa);
}
-static bool __mem_id_disconnect(int id, bool force)
+static bool __mem_id_disconnect(int id)
{
struct xdp_mem_allocator *xa;
bool safe_to_remove = true;
@@ -104,30 +104,26 @@ static bool __mem_id_disconnect(int id, bool force)
if (xa->mem.type == MEM_TYPE_PAGE_POOL)
safe_to_remove = page_pool_request_shutdown(xa->page_pool);
- trace_mem_disconnect(xa, safe_to_remove, force);
+ trace_mem_disconnect(xa, safe_to_remove);
- if ((safe_to_remove || force) &&
+ if ((safe_to_remove) &&
!rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
mutex_unlock(&mem_id_lock);
- return (safe_to_remove|force);
+ return safe_to_remove;
}
-#define DEFER_TIME (msecs_to_jiffies(1000))
-#define DEFER_WARN_INTERVAL (30 * HZ)
-#define DEFER_MAX_RETRIES 120
+#define DEFER_TIME (msecs_to_jiffies(1000UL))
+#define DEFER_WARN_INTERVAL (600UL * HZ)
static void mem_id_disconnect_defer_retry(struct work_struct *wq)
{
struct delayed_work *dwq = to_delayed_work(wq);
struct xdp_mem_allocator *xa = container_of(dwq, typeof(*xa), defer_wq);
- bool force = false;
+ unsigned long defer_time;
- if (xa->disconnect_cnt > DEFER_MAX_RETRIES)
- force = true;
-
- if (__mem_id_disconnect(xa->mem.id, force))
+ if (__mem_id_disconnect(xa->mem.id))
return;
/* Periodic warning */
@@ -140,7 +136,8 @@ static void mem_id_disconnect_defer_retry(struct work_struct *wq)
}
/* Still not ready to be disconnected, retry later */
- schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
+ defer_time = min(DEFER_WARN_INTERVAL, DEFER_TIME * xa->disconnect_cnt);
+ schedule_delayed_work(&xa->defer_wq, defer_time);
}
void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
@@ -161,7 +158,7 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
if (id == 0)
return;
- if (__mem_id_disconnect(id, false))
+ if (__mem_id_disconnect(id))
return;
/* Could not disconnect, defer new disconnect attempt to later */
@@ -402,15 +399,8 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
page = virt_to_head_page(data);
- if (likely(xa)) {
- napi_direct &= !xdp_return_frame_no_direct();
- page_pool_put_page(xa->page_pool, page, napi_direct);
- } else {
- /* Hopefully stack show who to blame for late return */
- WARN_ONCE(1, "page_pool gone mem.id=%d", mem->id);
- trace_mem_return_failed(mem, page);
- put_page(page);
- }
+ napi_direct &= !xdp_return_frame_no_direct();
+ page_pool_put_page(xa->page_pool, page, napi_direct);
rcu_read_unlock();
break;
case MEM_TYPE_PAGE_SHARED:
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