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SubjectRe: [PATCH] net: called rtnl_unlock() before runpm resumes devices
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Date
On 29.04.2021 13:58, Krzysztof Kozlowski wrote:
> On Tue, 20 Apr 2021 at 09:55, AceLan Kao <acelan.kao@canonical.com> wrote:
>>
>> From: "Chia-Lin Kao (AceLan)" <acelan.kao@canonical.com>
>>
>> The rtnl_lock() has been called in rtnetlink_rcv_msg(), and then in
>> __dev_open() it calls pm_runtime_resume() to resume devices, and in
>> some devices' resume function(igb_resum,igc_resume) they calls rtnl_lock()
>> again. That leads to a recursive lock.
>>
>> It should leave the devices' resume function to decide if they need to
>> call rtnl_lock()/rtnl_unlock(), so call rtnl_unlock() before calling
>> pm_runtime_resume() and then call rtnl_lock() after it in __dev_open().
>>
>> [ 967.723577] INFO: task ip:6024 blocked for more than 120 seconds.
>> [ 967.723588] Not tainted 5.12.0-rc3+ #1
>> [ 967.723592] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [ 967.723594] task:ip state:D stack: 0 pid: 6024 ppid: 5957 flags:0x00004000
>> [ 967.723603] Call Trace:
>> [ 967.723610] __schedule+0x2de/0x890
>> [ 967.723623] schedule+0x4f/0xc0
>> [ 967.723629] schedule_preempt_disabled+0xe/0x10
>> [ 967.723636] __mutex_lock.isra.0+0x190/0x510
>> [ 967.723644] __mutex_lock_slowpath+0x13/0x20
>> [ 967.723651] mutex_lock+0x32/0x40
>> [ 967.723657] rtnl_lock+0x15/0x20
>> [ 967.723665] igb_resume+0xee/0x1d0 [igb]
>> [ 967.723687] ? pci_pm_default_resume+0x30/0x30
>> [ 967.723696] igb_runtime_resume+0xe/0x10 [igb]
>> [ 967.723713] pci_pm_runtime_resume+0x74/0x90
>> [ 967.723718] __rpm_callback+0x53/0x1c0
>> [ 967.723725] rpm_callback+0x57/0x80
>> [ 967.723730] ? pci_pm_default_resume+0x30/0x30
>> [ 967.723735] rpm_resume+0x547/0x760
>> [ 967.723740] __pm_runtime_resume+0x52/0x80
>> [ 967.723745] __dev_open+0x56/0x160
>> [ 967.723753] ? _raw_spin_unlock_bh+0x1e/0x20
>> [ 967.723758] __dev_change_flags+0x188/0x1e0
>> [ 967.723766] dev_change_flags+0x26/0x60
>> [ 967.723773] do_setlink+0x723/0x10b0
>> [ 967.723782] ? __nla_validate_parse+0x5b/0xb80
>> [ 967.723792] __rtnl_newlink+0x594/0xa00
>> [ 967.723800] ? nla_put_ifalias+0x38/0xa0
>> [ 967.723807] ? __nla_reserve+0x41/0x50
>> [ 967.723813] ? __nla_reserve+0x41/0x50
>> [ 967.723818] ? __kmalloc_node_track_caller+0x49b/0x4d0
>> [ 967.723824] ? pskb_expand_head+0x75/0x310
>> [ 967.723830] ? nla_reserve+0x28/0x30
>> [ 967.723835] ? skb_free_head+0x25/0x30
>> [ 967.723843] ? security_sock_rcv_skb+0x2f/0x50
>> [ 967.723850] ? netlink_deliver_tap+0x3d/0x210
>> [ 967.723859] ? sk_filter_trim_cap+0xc1/0x230
>> [ 967.723863] ? skb_queue_tail+0x43/0x50
>> [ 967.723870] ? sock_def_readable+0x4b/0x80
>> [ 967.723876] ? __netlink_sendskb+0x42/0x50
>> [ 967.723888] ? security_capable+0x3d/0x60
>> [ 967.723894] ? __cond_resched+0x19/0x30
>> [ 967.723900] ? kmem_cache_alloc_trace+0x390/0x440
>> [ 967.723906] rtnl_newlink+0x49/0x70
>> [ 967.723913] rtnetlink_rcv_msg+0x13c/0x370
>> [ 967.723920] ? _copy_to_iter+0xa0/0x460
>> [ 967.723927] ? rtnl_calcit.isra.0+0x130/0x130
>> [ 967.723934] netlink_rcv_skb+0x55/0x100
>> [ 967.723939] rtnetlink_rcv+0x15/0x20
>> [ 967.723944] netlink_unicast+0x1a8/0x250
>> [ 967.723949] netlink_sendmsg+0x233/0x460
>> [ 967.723954] sock_sendmsg+0x65/0x70
>> [ 967.723958] ____sys_sendmsg+0x218/0x290
>> [ 967.723961] ? copy_msghdr_from_user+0x5c/0x90
>> [ 967.723966] ? lru_cache_add_inactive_or_unevictable+0x27/0xb0
>> [ 967.723974] ___sys_sendmsg+0x81/0xc0
>> [ 967.723980] ? __mod_memcg_lruvec_state+0x22/0xe0
>> [ 967.723987] ? kmem_cache_free+0x244/0x420
>> [ 967.723991] ? dentry_free+0x37/0x70
>> [ 967.723996] ? mntput_no_expire+0x4c/0x260
>> [ 967.724001] ? __cond_resched+0x19/0x30
>> [ 967.724007] ? security_file_free+0x54/0x60
>> [ 967.724013] ? call_rcu+0xa4/0x250
>> [ 967.724021] __sys_sendmsg+0x62/0xb0
>> [ 967.724026] ? exit_to_user_mode_prepare+0x3d/0x1a0
>> [ 967.724032] __x64_sys_sendmsg+0x1f/0x30
>> [ 967.724037] do_syscall_64+0x38/0x90
>> [ 967.724044] entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
>> ---
>> net/core/dev.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 1f79b9aa9a3f..427cbc80d1e5 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1537,8 +1537,11 @@ static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
>>
>> if (!netif_device_present(dev)) {
>> /* may be detached because parent is runtime-suspended */
>> - if (dev->dev.parent)
>> + if (dev->dev.parent) {
>> + rtnl_unlock();
>> pm_runtime_resume(dev->dev.parent);
>
> A side topic, maybe a little bit silly question (I don't know that
> much about net core):
> Why not increase the parent or current PM runtime usage counter
> instead? The problem with calling pm_runtime_resume() is that if the
> parent device was already suspended (so it's usage counter ==0), it
> might get suspended right after this call. IOW, you do not have any
> guarantee that the device will be really resumed. Probably it should
> be pm_runtime_resume_and_get() (and later "put" on close or other
> events). This however might not solve the lock problem at all.
>
The point of runtime-resuming the parent here isn't to ensure it's
resumed for the complete time the device is open. It's called
because netif_device_present() may be (initially) false just because
the parent is runtime-suspended.
We want the device to be able to runtime-suspend later if e.g.
the link is down.

> Best regards,
> Krzysztof
>

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