6.6-stable review patch. If anyone has any objections, please let me know.
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From: Dave Marquardt davemarq@linux.ibm.com
[ Upstream commit 053f3ff67d7feefc75797863f3d84b47ad47086f ]
v2: - Created a single error handling unlock and exit in veth_pool_store - Greatly expanded commit message with previous explanatory-only text
Summary: Use rtnl_mutex to synchronize veth_pool_store with itself, ibmveth_close and ibmveth_open, preventing multiple calls in a row to napi_disable.
Background: Two (or more) threads could call veth_pool_store through writing to /sys/devices/vio/30000002/pool*/*. You can do this easily with a little shell script. This causes a hang.
I configured LOCKDEP, compiled ibmveth.c with DEBUG, and built a new kernel. I ran this 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.
Signed-off-by: Dave Marquardt davemarq@linux.ibm.com Fixes: 860f242eb534 ("[PATCH] ibmveth change buffer pools dynamically") Reviewed-by: Nick Child nnac123@linux.ibm.com Reviewed-by: Simon Horman horms@kernel.org Link: https://patch.msgid.link/20250402154403.386744-1-davemarq@linux.ibm.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ethernet/ibm/ibmveth.c | 39 +++++++++++++++++++++--------- 1 file changed, 27 insertions(+), 12 deletions(-)
diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c index a8d79ee350f8d..a332a0e3154a2 100644 --- a/drivers/net/ethernet/ibm/ibmveth.c +++ b/drivers/net/ethernet/ibm/ibmveth.c @@ -1824,18 +1824,22 @@ 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"); - return -ENOMEM; + rc = -ENOMEM; + goto unlock_err; } pool->active = 1; ibmveth_close(netdev); - if ((rc = ibmveth_open(netdev))) - return rc; + rc = ibmveth_open(netdev); + if (rc) + goto unlock_err; } else { pool->active = 1; } @@ -1855,48 +1859,59 @@ 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"); - return -EPERM; + rc = -EPERM; + goto unlock_err; }
if (netif_running(netdev)) { ibmveth_close(netdev); pool->active = 0; - if ((rc = ibmveth_open(netdev))) - return rc; + rc = ibmveth_open(netdev); + if (rc) + goto unlock_err; } pool->active = 0; } } else if (attr == &veth_num_attr) { if (value <= 0 || value > IBMVETH_MAX_POOL_COUNT) { - return -EINVAL; + rc = -EINVAL; + goto unlock_err; } else { if (netif_running(netdev)) { ibmveth_close(netdev); pool->size = value; - if ((rc = ibmveth_open(netdev))) - return rc; + rc = ibmveth_open(netdev); + if (rc) + goto unlock_err; } else { pool->size = value; } } } else if (attr == &veth_size_attr) { if (value <= IBMVETH_BUFF_OH || value > IBMVETH_MAX_BUF_SIZE) { - return -EINVAL; + rc = -EINVAL; + goto unlock_err; } else { if (netif_running(netdev)) { ibmveth_close(netdev); pool->buff_size = value; - if ((rc = ibmveth_open(netdev))) - return rc; + rc = ibmveth_open(netdev); + if (rc) + goto unlock_err; } else { pool->buff_size = value; } } } + rtnl_unlock();
/* kick the interrupt handler to allocate/deallocate pools */ ibmveth_interrupt(netdev->irq, netdev); return count; + +unlock_err: + rtnl_unlock(); + return rc; }