From: Martin Wilck mwilck@suse.com

We have observed a few crashes run_timer_softirq(), where a broken timer_list struct belonging to an anatt_timer was encountered. The broken structures look like this, and we see actually multiple ones attached to the same timer base:

crash> struct timer_list 0xffff92471bcfdc90 struct timer_list { entry = { next = 0xdead000000000122, // LIST_POISON2 pprev = 0x0 }, expires = 4296022933, function = 0xffffffffc06de5e0 <nvme_anatt_timeout>, flags = 20 }

If such a timer is encountered in run_timer_softirq(), the kernel crashes. The test scenario was an I/O load test with lots of NVMe controllers, some of which were removed and re-added on the storage side.

I think this may happen if the rdma recovery_work starts, in this call chain:

nvme_rdma_error_recovery_work() /* this stops all sorts of activity for the controller, but not the multipath-related work queue and timer */ nvme_rdma_reconnect_or_remove(ctrl) => kicks reconnect_work

work queue: reconnect_work

nvme_rdma_reconnect_ctrl_work() nvme_rdma_setup_ctrl() nvme_rdma_configure_admin_queue() nvme_init_identify() nvme_mpath_init() # this sets some fields of the timer_list without taking a lock timer_setup() nvme_read_ana_log() mod_timer() or del_timer_sync()

Similar for TCP. The idea for the patch is based on the observation that nvme_rdma_reset_ctrl_work() calls nvme_stop_ctrl()->nvme_mpath_stop(), whereas nvme_rdma_error_recovery_work() stops only the keepalive timer, but not the anatt timer. Also, nvme_mpath_init() is the only place where the anatt_timer structure is accessed without locking.

[The following paragraph was contributed by Chao Leng lengchao@huawei.com]

The process maybe:1.ana_work add the timer;2.error recovery occurs, in reconnecting, reinitialize the timer and call nvme_read_ana_log, nvme_read_ana_log may add the timer again. The same timer is added twice, crash will happens later.

This situation has actually been observed in a crash dump, where we found an anatt timer pending that had been started ~80s ago, despite a log message telling that the anatt timer for the same controller had timed out a few seconds ago. This could only be explained by the same timer having been attached multiple times.

Signed-off-by: Martin Wilck mwilck@suse.com Reviewed-by: Sagi Grimberg sagi@grimberg.me Reviewed-by: Chao Leng lengchao@huawei.com Cc: stable@vger.kernel.org

---- Changes in v4: Updated commit message with Chao Leng's analysis, as suggested by Daniel Wagner.

Changes in v3: Changed the subject line, as suggested by Sagi Grimberg

Changes in v2: Moved call to nvme_mpath_stop() further down, directly before the call of nvme_rdma_reconnect_or_remove() (Chao Leng) --- drivers/nvme/host/multipath.c | 1 + drivers/nvme/host/rdma.c | 1 + drivers/nvme/host/tcp.c | 1 + 3 files changed, 3 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c index a1d476e1ac02..c63dd5dfa7ff 100644 --- a/drivers/nvme/host/multipath.c +++ b/drivers/nvme/host/multipath.c @@ -586,6 +586,7 @@ void nvme_mpath_stop(struct nvme_ctrl *ctrl) del_timer_sync(&ctrl->anatt_timer); cancel_work_sync(&ctrl->ana_work); } +EXPORT_SYMBOL_GPL(nvme_mpath_stop);

#define SUBSYS_ATTR_RW(_name, _mode, _show, _store) \ struct device_attribute subsys_attr_##_name = \ diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c index be905d4fdb47..fc07a7b0dc1d 100644 --- a/drivers/nvme/host/rdma.c +++ b/drivers/nvme/host/rdma.c @@ -1202,6 +1202,7 @@ static void nvme_rdma_error_recovery_work(struct work_struct *work) return; }

+ nvme_mpath_stop(&ctrl->ctrl); nvme_rdma_reconnect_or_remove(ctrl); }

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c index a0f00cb8f9f3..46287b4f4d10 100644 --- a/drivers/nvme/host/tcp.c +++ b/drivers/nvme/host/tcp.c @@ -2068,6 +2068,7 @@ static void nvme_tcp_error_recovery_work(struct work_struct *work) return; }

+ nvme_mpath_stop(ctrl); nvme_tcp_reconnect_or_remove(ctrl); }