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Message-ID: <20250331212328.109496-1-davemarq@linux.ibm.com>
Date: Mon, 31 Mar 2025 16:23:28 -0500
From: davemarq@...ux.ibm.com
To: netdev@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org, Dave Marquardt <davemarq@...ux.ibm.com>,
Nick Child <nnac123@...ux.ibm.com>
Subject: [PATCH net] net: ibmveth: make veth_pool_store stop hanging
From: Dave Marquardt <davemarq@...ux.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 <davemarq@...ux.ibm.com>
Fixes: 860f242eb534 ("[PATCH] ibmveth change buffer pools dynamically")
Reviewed-by: Nick Child <nnac123@...ux.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.
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;
+ }
} else {
pool->active = 1;
}
@@ -1833,44 +1839,57 @@ static ssize_t veth_pool_store(struct kobject *kobj, struct attribute *attr,
if (i == IBMVETH_NUM_BUFF_POOLS) {
netdev_err(netdev, "no active pool >= MTU\n");
+ rtnl_unlock();
return -EPERM;
}
if (netif_running(netdev)) {
ibmveth_close(netdev);
pool->active = 0;
- if ((rc = ibmveth_open(netdev)))
+ rc = ibmveth_open(netdev);
+ if (rc) {
+ rtnl_unlock();
return rc;
+ }
}
pool->active = 0;
}
} else if (attr == &veth_num_attr) {
if (value <= 0 || value > IBMVETH_MAX_POOL_COUNT) {
+ rtnl_unlock();
return -EINVAL;
} else {
if (netif_running(netdev)) {
ibmveth_close(netdev);
pool->size = value;
- if ((rc = ibmveth_open(netdev)))
+ rc = ibmveth_open(netdev);
+ if (rc) {
+ rtnl_unlock();
return rc;
+ }
} else {
pool->size = value;
}
}
} else if (attr == &veth_size_attr) {
if (value <= IBMVETH_BUFF_OH || value > IBMVETH_MAX_BUF_SIZE) {
+ rtnl_unlock();
return -EINVAL;
} else {
if (netif_running(netdev)) {
ibmveth_close(netdev);
pool->buff_size = value;
- if ((rc = ibmveth_open(netdev)))
+ rc = ibmveth_open(netdev);
+ if (rc) {
+ rtnl_unlock();
return rc;
+ }
} else {
pool->buff_size = value;
}
}
}
+ rtnl_unlock();
/* kick the interrupt handler to allocate/deallocate pools */
ibmveth_interrupt(netdev->irq, netdev);
base-commit: 4f1eaabb4b66a1f7473f584e14e15b2ac19dfaf3
--
2.49.0
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