On 2020/11/3 12:12, Ming Lei wrote:
On Mon, Nov 02, 2020 at 10:07:57PM -0500, xiubli@xxxxxxxxxx wrote:From: Xiubo Li <xiubli@xxxxxxxxxx> The crash call trace: <6>[ 1012.319386] block nbd1: NBD_DISCONNECT <1>[ 1012.319437] BUG: kernel NULL pointer dereference, address: 0000000000000020 <1>[ 1012.319439] #PF: supervisor write access in kernel mode <1>[ 1012.319441] #PF: error_code(0x0002) - not-present page <6>[ 1012.319442] PGD 0 P4D 0 <4>[ 1012.319448] Oops: 0002 [#1] SMP NOPTI <4>[ 1012.319454] CPU: 9 PID: 25111 Comm: rbd-nbd Tainted: G E 5.9.0+ #6 [...] <4>[ 1012.319505] PKRU: 55555554 <4>[ 1012.319506] Call Trace: <4>[ 1012.319560] flush_workqueue+0x81/0x440 <4>[ 1012.319598] nbd_disconnect_and_put+0x50/0x70 [nbd] <4>[ 1012.319607] nbd_genl_disconnect+0xc7/0x170 [nbd] <4>[ 1012.319627] genl_rcv_msg+0x1dd/0x2f9 <4>[ 1012.319642] ? genl_start+0x140/0x140 <4>[ 1012.319644] netlink_rcv_skb+0x49/0x110 <4>[ 1012.319649] genl_rcv+0x24/0x40 <4>[ 1012.319651] netlink_unicast+0x1a5/0x280 <4>[ 1012.319653] netlink_sendmsg+0x23d/0x470 <4>[ 1012.319667] sock_sendmsg+0x5b/0x60 <4>[ 1012.319676] ____sys_sendmsg+0x1ef/0x260 <4>[ 1012.319679] ? copy_msghdr_from_user+0x5c/0x90 <4>[ 1012.319680] ? ____sys_recvmsg+0xa5/0x180 <4>[ 1012.319682] ___sys_sendmsg+0x7c/0xc0 <4>[ 1012.319683] ? copy_msghdr_from_user+0x5c/0x90 <4>[ 1012.319685] ? ___sys_recvmsg+0x89/0xc0 <4>[ 1012.319692] ? __wake_up_common_lock+0x87/0xc0 <4>[ 1012.319715] ? __check_object_size+0x46/0x173 <4>[ 1012.319727] ? _copy_to_user+0x22/0x30 <4>[ 1012.319729] ? move_addr_to_user+0xc3/0x100 <4>[ 1012.319731] __sys_sendmsg+0x57/0xa0 <4>[ 1012.319744] do_syscall_64+0x33/0x40 <4>[ 1012.319760] entry_SYSCALL_64_after_hwframe+0x44/0xa9 <4>[ 1012.319780] RIP: 0033:0x7f5baa8e3ad5 In case the reference of nbd->config has reached zero and the related resource has been released, if another process tries to send the DISCONENCT cmd by using the netlink, it will potentially crash like this. Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx> --- drivers/block/nbd.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index f46e26c9d9b3..3bb8281bb753 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2003,16 +2003,31 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)static void nbd_disconnect_and_put(struct nbd_device *nbd){ + bool flush = true; + mutex_lock(&nbd->config_lock); nbd_disconnect(nbd); nbd_clear_sock(nbd); - mutex_unlock(&nbd->config_lock); /* - * Make sure recv thread has finished, so it does not drop the last - * config ref and try to destroy the workqueue from inside the work - * queue. + * In very rare case that the nbd->recv_workq may already have been + * released by the recv_work(). */ - flush_workqueue(nbd->recv_workq); + if (likely(!nbd->recv_workq))It is actually unlikely, but doesn't make any sense to annotate the check since it isn't fast path, so please remove it.
Sure, will do it. Thanks.
+ refcount_inc(&nbd->config_refs); + else + flush = false; + mutex_unlock(&nbd->config_lock); + + if (flush) { + /* + * Make sure recv thread has finished, so it does not drop + * the last config ref and try to destroy the workqueue + * from inside the work queue. + */ + flush_workqueue(nbd->recv_workq); + nbd_config_put(nbd); + } + if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, &nbd->config->runtime_flags)) nbd_config_put(nbd);The approach is fine, and the reason is that nbd_disconnect_and_put() still can be called via netlink when the nbd device has been closed: Once the above likely() is removed, feel free to add: Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> Thanks, Ming
