On 3/31/25 11:23 PM, davem...@linux.ibm.com wrote: > From: Dave Marquardt <davem...@linux.ibm.com> > > Use rtnl_mutex to synchronize veth_pool_store with itself, > ibmveth_close and ibmveth_open, preventing multiple calls in a row to > napi_disable. > > Signed-off-by: Dave Marquardt <davem...@linux.ibm.com> > Fixes: 860f242eb534 ("[PATCH] ibmveth change buffer pools dynamically") > Reviewed-by: Nick Child <nnac...@linux.ibm.com> > --- > In working on removing BUG_ON calls from ibmveth, I realized that 2 > threads could call veth_pool_store through writing to > /sys/devices/vio/30000002/pool*/*. You can do this easily with a little > shell script. > > Running on a 6.14 kernel, I saw a hang: > > [ 243.683282][ T108] INFO: task stress.sh:5829 blocked for more than > 122 seconds. > [ 243.683300][ T108] Not tainted 6.14.0-01103-g2df0c02dab82 #3 > [ 243.683303][ T108] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 366.563278][ T108] INFO: task stress.sh:5829 blocked for more than > 245 seconds. > [ 366.563297][ T108] Not tainted 6.14.0-01103-g2df0c02dab82 #3 > [ 366.563301][ T108] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > > I configured LOCKDEP, compiled ibmveth.c with DEBUG, and built a new > kernel. I ran the test again and saw: > > Setting pool0/active to 0 > Setting pool1/active to 1 > [ 73.911067][ T4365] ibmveth 30000002 eth0: close starting > Setting pool1/active to 1 > Setting pool1/active to 0 > [ 73.911367][ T4366] ibmveth 30000002 eth0: close starting > [ 73.916056][ T4365] ibmveth 30000002 eth0: close complete > [ 73.916064][ T4365] ibmveth 30000002 eth0: open starting > [ 110.808564][ T712] systemd-journald[712]: Sent WATCHDOG=1 > notification. > [ 230.808495][ T712] systemd-journald[712]: Sent WATCHDOG=1 > notification. > [ 243.683786][ T123] INFO: task stress.sh:4365 blocked for more than > 122 seconds. > [ 243.683827][ T123] Not tainted 6.14.0-01103-g2df0c02dab82-dirty > #8 > [ 243.683833][ T123] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 243.683838][ T123] task:stress.sh state:D stack:28096 pid:4365 > tgid:4365 ppid:4364 task_flags:0x400040 flags:0x00042000 > [ 243.683852][ T123] Call Trace: > [ 243.683857][ T123] [c00000000c38f690] [0000000000000001] 0x1 > (unreliable) > [ 243.683868][ T123] [c00000000c38f840] [c00000000001f908] > __switch_to+0x318/0x4e0 > [ 243.683878][ T123] [c00000000c38f8a0] [c000000001549a70] > __schedule+0x500/0x12a0 > [ 243.683888][ T123] [c00000000c38f9a0] [c00000000154a878] > schedule+0x68/0x210 > [ 243.683896][ T123] [c00000000c38f9d0] [c00000000154ac80] > schedule_preempt_disabled+0x30/0x50 > [ 243.683904][ T123] [c00000000c38fa00] [c00000000154dbb0] > __mutex_lock+0x730/0x10f0 > [ 243.683913][ T123] [c00000000c38fb10] [c000000001154d40] > napi_enable+0x30/0x60 > [ 243.683921][ T123] [c00000000c38fb40] [c000000000f4ae94] > ibmveth_open+0x68/0x5dc > [ 243.683928][ T123] [c00000000c38fbe0] [c000000000f4aa20] > veth_pool_store+0x220/0x270 > [ 243.683936][ T123] [c00000000c38fc70] [c000000000826278] > sysfs_kf_write+0x68/0xb0 > [ 243.683944][ T123] [c00000000c38fcb0] [c0000000008240b8] > kernfs_fop_write_iter+0x198/0x2d0 > [ 243.683951][ T123] [c00000000c38fd00] [c00000000071b9ac] > vfs_write+0x34c/0x650 > [ 243.683958][ T123] [c00000000c38fdc0] [c00000000071bea8] > ksys_write+0x88/0x150 > [ 243.683966][ T123] [c00000000c38fe10] [c0000000000317f4] > system_call_exception+0x124/0x340 > [ 243.683973][ T123] [c00000000c38fe50] [c00000000000d05c] > system_call_vectored_common+0x15c/0x2ec > ... > [ 243.684087][ T123] Showing all locks held in the system: > [ 243.684095][ T123] 1 lock held by khungtaskd/123: > [ 243.684099][ T123] #0: c00000000278e370 (rcu_read_lock){....}-{1:2}, > at: debug_show_all_locks+0x50/0x248 > [ 243.684114][ T123] 4 locks held by stress.sh/4365: > [ 243.684119][ T123] #0: c00000003a4cd3f8 (sb_writers#3){.+.+}-{0:0}, > at: ksys_write+0x88/0x150 > [ 243.684132][ T123] #1: c000000041aea888 (&of->mutex#2){+.+.}-{3:3}, > at: kernfs_fop_write_iter+0x154/0x2d0 > [ 243.684143][ T123] #2: c0000000366fb9a8 (kn->active#64){.+.+}-{0:0}, > at: kernfs_fop_write_iter+0x160/0x2d0 > [ 243.684155][ T123] #3: c000000035ff4cb8 (&dev->lock){+.+.}-{3:3}, > at: napi_enable+0x30/0x60 > [ 243.684166][ T123] 5 locks held by stress.sh/4366: > [ 243.684170][ T123] #0: c00000003a4cd3f8 (sb_writers#3){.+.+}-{0:0}, > at: ksys_write+0x88/0x150 > [ 243.684183][ T123] #1: c00000000aee2288 (&of->mutex#2){+.+.}-{3:3}, > at: kernfs_fop_write_iter+0x154/0x2d0 > [ 243.684194][ T123] #2: c0000000366f4ba8 (kn->active#64){.+.+}-{0:0}, > at: kernfs_fop_write_iter+0x160/0x2d0 > [ 243.684205][ T123] #3: c000000035ff4cb8 (&dev->lock){+.+.}-{3:3}, > at: napi_disable+0x30/0x60 > [ 243.684216][ T123] #4: c0000003ff9bbf18 (&rq->__lock){-.-.}-{2:2}, > at: __schedule+0x138/0x12a0 > > From the ibmveth debug, two threads are calling veth_pool_store, which > calls ibmveth_close and ibmveth_open. Here's the sequence: > > T4365 T4366 > ----------------- ----------------- --------- > veth_pool_store veth_pool_store > ibmveth_close > ibmveth_close > napi_disable > napi_disable > ibmveth_open > napi_enable <- HANG > > ibmveth_close calls napi_disable at the top and ibmveth_open calls > napi_enable at the top. > > https://docs.kernel.org/networking/napi.html]] says > > The control APIs are not idempotent. Control API calls are safe > against concurrent use of datapath APIs but an incorrect sequence of > control API calls may result in crashes, deadlocks, or race > conditions. For example, calling napi_disable() multiple times in a > row will deadlock. > > In the normal open and close paths, rtnl_mutex is acquired to prevent > other callers. This is missing from veth_pool_store. Use rtnl_mutex in > veth_pool_store fixes these hangs.
Some/most of the above should actually land into the commit message, please rewrite it accordingly. > drivers/net/ethernet/ibm/ibmveth.c | 27 +++++++++++++++++++++++---- > 1 file changed, 23 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/ethernet/ibm/ibmveth.c > b/drivers/net/ethernet/ibm/ibmveth.c > index b619a3ec245b..77ef19a53e72 100644 > --- a/drivers/net/ethernet/ibm/ibmveth.c > +++ b/drivers/net/ethernet/ibm/ibmveth.c > @@ -1802,18 +1802,24 @@ static ssize_t veth_pool_store(struct kobject *kobj, > struct attribute *attr, > long value = simple_strtol(buf, NULL, 10); > long rc; > > + rtnl_lock(); > + > if (attr == &veth_active_attr) { > if (value && !pool->active) { > if (netif_running(netdev)) { > if (ibmveth_alloc_buffer_pool(pool)) { > netdev_err(netdev, > "unable to alloc pool\n"); > + rtnl_unlock(); > return -ENOMEM; > } > pool->active = 1; > ibmveth_close(netdev); > - if ((rc = ibmveth_open(netdev))) > + rc = ibmveth_open(netdev); > + if (rc) { > + rtnl_unlock(); > return rc; If you avoid a bit of duplicate code with goto unlock_err; // at the end of the function unlock_err: rtnl_unlock(); return rc; Cheers, Paolo