kernel/linux.git/net/core/netpoll.c, branch v5.10.257

net: netpoll: fix incorrect refcount handling causing incorrect cleanup

2025-12-06T21:08:21+00:00

[ Upstream commit 49c8d2c1f94cc2f4d1a108530d7ba52614b874c2 ] commit efa95b01da18 ("netpoll: fix use after free") incorrectly ignored the refcount and prematurely set dev->npinfo to NULL during netpoll cleanup, leading to improper behavior and memory leaks. Scenario causing lack of proper cleanup: 1) A netpoll is associated with a NIC (e.g., eth0) and netdev->npinfo is allocated, and refcnt = 1 - Keep in mind that npinfo is shared among all netpoll instances. In this case, there is just one. 2) Another netpoll is also associated with the same NIC and npinfo->refcnt += 1. - Now dev->npinfo->refcnt = 2; - There is just one npinfo associated to the netdev. 3) When the first netpolls goes to clean up: - The first cleanup succeeds and clears np->dev->npinfo, ignoring refcnt. - It basically calls `RCU_INIT_POINTER(np->dev->npinfo, NULL);` - Set dev->npinfo = NULL, without proper cleanup - No ->ndo_netpoll_cleanup() is either called 4) Now the second target tries to clean up - The second cleanup fails because np->dev->npinfo is already NULL. * In this case, ops->ndo_netpoll_cleanup() was never called, and the skb pool is not cleaned as well (for the second netpoll instance) - This leaks npinfo and skbpool skbs, which is clearly reported by kmemleak. Revert commit efa95b01da18 ("netpoll: fix use after free") and adds clarifying comments emphasizing that npinfo cleanup should only happen once the refcount reaches zero, ensuring stable and correct netpoll behavior. Cc: # 3.17.x Cc: Jay Vosburgh Fixes: efa95b01da18 ("netpoll: fix use after free") Signed-off-by: Breno Leitao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20251107-netconsole_torture-v10-1-749227b55f63@debian.org Signed-off-by: Jakub Kicinski [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

netpoll: prevent hanging NAPI when netcons gets enabled

2025-08-28T14:22:37+00:00

[ Upstream commit 2da4def0f487f24bbb0cece3bb2bcdcb918a0b72 ] Paolo spotted hangs in NIPA running driver tests against virtio. The tests hang in virtnet_close() -> virtnet_napi_tx_disable(). The problem is only reproducible if running multiple of our tests in sequence (I used TEST_PROGS="xdp.py ping.py netcons_basic.sh \ netpoll_basic.py stats.py"). Initial suspicion was that this is a simple case of double-disable of NAPI, but instrumenting the code reveals: Deadlocked on NAPI ffff888007cd82c0 (virtnet_poll_tx): state: 0x37, disabled: false, owner: 0, listed: false, weight: 64 The NAPI was not in fact disabled, owner is 0 (rather than -1), so the NAPI "thinks" it's scheduled for CPU 0 but it's not listed (!list_empty(&n->poll_list) => false). It seems odd that normal NAPI processing would wedge itself like this. Better suspicion is that netpoll gets enabled while NAPI is polling, and also grabs the NAPI instance. This confuses napi_complete_done(): [netpoll] [normal NAPI] napi_poll() have = netpoll_poll_lock() rcu_access_pointer(dev->npinfo) return NULL # no netpoll __napi_poll() ->poll(->weight) poll_napi() cmpxchg(->poll_owner, -1, cpu) poll_one_napi() set_bit(NAPI_STATE_NPSVC, ->state) napi_complete_done() if (NAPIF_STATE_NPSVC) return false # exit without clearing SCHED This feels very unlikely, but perhaps virtio has some interactions with the hypervisor in the NAPI ->poll that makes the race window larger? Best I could to to prove the theory was to add and trigger this warning in napi_poll (just before netpoll_poll_unlock()): WARN_ONCE(!have && rcu_access_pointer(n->dev->npinfo) && napi_is_scheduled(n) && list_empty(&n->poll_list), "NAPI race with netpoll %px", n); If this warning hits the next virtio_close() will hang. This patch survived 30 test iterations without a hang (without it the longest clean run was around 10). Credit for triggering this goes to Breno's recent netconsole tests. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Paolo Abeni Link: https://lore.kernel.org/c5a93ed1-9abe-4880-a3bb-8d1678018b1d@redhat.com Acked-by: Jason Wang Reviewed-by: Xuan Zhuo Link: https://patch.msgid.link/20250726010846.1105875-1-kuba@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: hold rcu read lock in __netpoll_send_skb()

2025-04-10T12:30:48+00:00

[ Upstream commit 505ead7ab77f289f12d8a68ac83da068e4d4408b ] The function __netpoll_send_skb() is being invoked without holding the RCU read lock. This oversight triggers a warning message when CONFIG_PROVE_RCU_LIST is enabled: net/core/netpoll.c:330 suspicious rcu_dereference_check() usage! netpoll_send_skb netpoll_send_udp write_ext_msg console_flush_all console_unlock vprintk_emit To prevent npinfo from disappearing unexpectedly, ensure that __netpoll_send_skb() is protected with the RCU read lock. Fixes: 2899656b494dcd1 ("netpoll: take rcu_read_lock_bh() in netpoll_send_skb_on_dev()") Signed-off-by: Breno Leitao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20250306-netpoll_rcu_v2-v2-1-bc4f5c51742a@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: Use rcu_access_pointer() in __netpoll_setup

2024-12-14T18:48:30+00:00

[ Upstream commit c69c5e10adb903ae2438d4f9c16eccf43d1fcbc1 ] The ndev->npinfo pointer in __netpoll_setup() is RCU-protected but is being accessed directly for a NULL check. While no RCU read lock is held in this context, we should still use proper RCU primitives for consistency and correctness. Replace the direct NULL check with rcu_access_pointer(), which is the appropriate primitive when only checking for NULL without dereferencing the pointer. This function provides the necessary ordering guarantees without requiring RCU read-side protection. Reviewed-by: Michal Kubiak Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20241118-netpoll_rcu-v1-1-a1888dcb4a02@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: Fix race condition in netpoll_owner_active

2024-07-05T07:12:35+00:00

[ Upstream commit c2e6a872bde9912f1a7579639c5ca3adf1003916 ] KCSAN detected a race condition in netpoll: BUG: KCSAN: data-race in net_rx_action / netpoll_send_skb write (marked) to 0xffff8881164168b0 of 4 bytes by interrupt on cpu 10: net_rx_action (./include/linux/netpoll.h:90 net/core/dev.c:6712 net/core/dev.c:6822) read to 0xffff8881164168b0 of 4 bytes by task 1 on cpu 2: netpoll_send_skb (net/core/netpoll.c:319 net/core/netpoll.c:345 net/core/netpoll.c:393) netpoll_send_udp (net/core/netpoll.c:?) value changed: 0x0000000a -> 0xffffffff This happens because netpoll_owner_active() needs to check if the current CPU is the owner of the lock, touching napi->poll_owner non atomically. The ->poll_owner field contains the current CPU holding the lock. Use an atomic read to check if the poll owner is the current CPU. Signed-off-by: Breno Leitao Link: https://lore.kernel.org/r/20240429100437.3487432-1-leitao@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

net: don't let netpoll invoke NAPI if in xmit context

2023-04-20T10:10:21+00:00

[ Upstream commit 275b471e3d2daf1472ae8fa70dc1b50c9e0b9e75 ] Commit 0db3dc73f7a3 ("[NETPOLL]: tx lock deadlock fix") narrowed down the region under netif_tx_trylock() inside netpoll_send_skb(). (At that point in time netif_tx_trylock() would lock all queues of the device.) Taking the tx lock was problematic because driver's cleanup method may take the same lock. So the change made us hold the xmit lock only around xmit, and expected the driver to take care of locking within ->ndo_poll_controller(). Unfortunately this only works if netpoll isn't itself called with the xmit lock already held. Netpoll code is careful and uses trylock(). The drivers, however, may be using plain lock(). Printing while holding the xmit lock is going to result in rare deadlocks. Luckily we record the xmit lock owners, so we can scan all the queues, the same way we scan NAPI owners. If any of the xmit locks is held by the local CPU we better not attempt any polling. It would be nice if we could narrow down the check to only the NAPIs and the queue we're trying to use. I don't see a way to do that now. Reported-by: Roman Gushchin Fixes: 0db3dc73f7a3 ("[NETPOLL]: tx lock deadlock fix") Signed-off-by: Jakub Kicinski Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Sasha Levin

net: Have netpoll bring-up DSA management interface

2020-11-18T19:04:11+00:00

DSA network devices rely on having their DSA management interface up and running otherwise their ndo_open() will return -ENETDOWN. Without doing this it would not be possible to use DSA devices as netconsole when configured on the command line. These devices also do not utilize the upper/lower linking so the check about the netpoll device having upper is not going to be a problem. The solution adopted here is identical to the one done for net/ipv4/ipconfig.c with 728c02089a0e ("net: ipv4: handle DSA enabled master network devices"), with the network namespace scope being restricted to that of the process configuring netpoll. Fixes: 04ff53f96a93 ("net: dsa: Add netconsole support") Tested-by: Vladimir Oltean Signed-off-by: Florian Fainelli Link: https://lore.kernel.org/r/20201117035236.22658-1-f.fainelli@gmail.com Signed-off-by: Jakub Kicinski

net: make sure napi_list is safe for RCU traversal

2020-09-10T20:08:46+00:00

netpoll needs to traverse dev->napi_list under RCU, make sure it uses the right iterator and that removal from this list is handled safely. Signed-off-by: Jakub Kicinski Signed-off-by: David S. Miller

net: disable netpoll on fresh napis

2020-08-26T23:16:39+00:00

napi_disable() makes sure to set the NAPI_STATE_NPSVC bit to prevent netpoll from accessing rings before init is complete. However, the same is not done for fresh napi instances in netif_napi_add(), even though we expect NAPI instances to be added as disabled. This causes crashes during driver reconfiguration (enabling XDP, changing the channel count) - if there is any printk() after netif_napi_add() but before napi_enable(). To ensure memory ordering is correct we need to use RCU accessors. Reported-by: Rob Sherwood Fixes: 2d8bff12699a ("netpoll: Close race condition between poll_one_napi and napi_disable") Signed-off-by: Jakub Kicinski Signed-off-by: David S. Miller

netpoll: accept NULL np argument in netpoll_send_skb()

2020-05-08T01:11:07+00:00

netpoll_send_skb() callers seem to leak skb if the np pointer is NULL. While this should not happen, we can make the code more robust. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller