kernel 各个模块的锁的设计
为什么 scsi_host_eh_past_deadline 成功之后，需要调用 scsi_device_put
if (scsi_host_eh_past_deadline(shost)) {
SCSI_LOG_ERROR_RECOVERY(3,
sdev_printk(KERN_INFO, sdev,
"%s: skip START_UNIT, past eh deadline\n",
current->comm));
scsi_device_put(sdev);
irq 的 lock 设计
- synchronize_irq
/**
* synchronize_irq - wait for pending IRQ handlers (on other CPUs)
* @irq: interrupt number to wait for
*
* This function waits for any pending IRQ handlers for this interrupt
* to complete before returning. If you use this function while
* holding a resource the IRQ handler may need you will deadlock.
*
* Can only be called from preemptible code as it might sleep when
* an interrupt thread is associated to @irq.
*
* It optionally makes sure (when the irq chip supports that method)
* that the interrupt is not pending in any CPU and waiting for
* service.
*/
void synchronize_irq(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
if (desc)
__synchronize_irq(desc);
}
如果一直来中断，那这个还可以删掉吗? 还是说 spurious 中断其实根本就不在乎的 只要当前正在处理的中断可以解决就可以了。
2.
- handle_irq_event_percpu
- note_interrupt
- report_bad_irq
- __report_bad_irq
- report_bad_irq
- note_interrupt
有一个注释:
/*
* We need to take desc->lock here. note_interrupt() is called
* w/o desc->lock held, but IRQ_PROGRESS set. We might race
* with something else removing an action. It's ok to take
* desc->lock here. See synchronize_irq().
*/
raw_spin_lock_irqsave(&desc->lock, flags);
for_each_action_of_desc(desc, action) {
printk(KERN_ERR "[<%p>] %ps", action->handler, action->handler);
if (action->thread_fn)
printk(KERN_CONT " threaded [<%p>] %ps",
action->thread_fn, action->thread_fn);
printk(KERN_CONT "\n");
}
raw_spin_unlock_irqrestore(&desc->lock, flags);
也就是，通过 IRQ_PROGRESS 这个 flag 就可以保证 desc 不会被释放。
- irq_domain_free_irqs 的时候，如果当时正好有中断，如何?
的确都是在考虑的范围之类的
@[
__synchronize_irq+1
irq_domain_free_irqs+144
msi_domain_free_locked.part.0+397
msi_domain_free_irqs_all_locked+107
pci_free_msi_irqs+18
pci_disable_msix+76
pci_free_irq_vectors+19
nvme_setup_io_queues+509
nvme_probe.cold+353
local_pci_probe+63
pci_device_probe+216
really_probe+201
__driver_probe_device+120
driver_probe_device+31
__device_attach_driver+137
bus_for_each_drv+151
__device_attach+177
pci_bus_add_device+88
pci_bus_add_devices+48
enable_slot+854
acpiphp_check_bridge.part.0+335
acpiphp_hotplug_notify+378
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 1
@[
__synchronize_irq+1
free_irq+297
pci_free_irq+28
nvme_setup_io_queues+1836
nvme_probe.cold+353
local_pci_probe+63
pci_device_probe+216
really_probe+201
__driver_probe_device+120
driver_probe_device+31
__device_attach_driver+137
bus_for_each_drv+151
__device_attach+177
pci_bus_add_device+88
pci_bus_add_devices+48
enable_slot+854
acpiphp_check_bridge.part.0+335
acpiphp_hotplug_notify+378
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 1
@[
__synchronize_irq+1
nvme_poll_irqdisable+69
nvme_dev_disable+224
nvme_remove+111
pci_device_remove+63
device_release_driver_internal+422
pci_stop_bus_device+109
pci_stop_and_remove_bus_device+18
disable_slot+101
acpiphp_disable_and_eject_slot+20
acpiphp_hotplug_notify+317
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 1
@[
__synchronize_irq+1
free_irq+297
pci_free_irq+28
nvme_dev_disable+293
nvme_remove+111
pci_device_remove+63
device_release_driver_internal+422
pci_stop_bus_device+109
pci_stop_and_remove_bus_device+18
disable_slot+101
acpiphp_disable_and_eject_slot+20
acpiphp_hotplug_notify+317
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 1
@[
__synchronize_irq+1
free_irq+297
pci_free_irq+28
nvme_dev_disable+277
nvme_remove+111
pci_device_remove+63
device_release_driver_internal+422
pci_stop_bus_device+109
pci_stop_and_remove_bus_device+18
disable_slot+101
acpiphp_disable_and_eject_slot+20
acpiphp_hotplug_notify+317
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 64
@[
__synchronize_irq+1
irq_domain_free_irqs+144
msi_domain_free_locked.part.0+397
msi_domain_free_irqs_all_locked+107
pci_free_msi_irqs+18
pci_disable_msix+76
pci_free_irq_vectors+19
nvme_dev_disable+305
nvme_remove+111
pci_device_remove+63
device_release_driver_internal+422
pci_stop_bus_device+109
pci_stop_and_remove_bus_device+18
disable_slot+101
acpiphp_disable_and_eject_slot+20
acpiphp_hotplug_notify+317
acpi_device_hotplug+262
acpi_hotplug_work_fn+30
process_one_work+501
worker_thread+444
kthread+254
ret_from_fork+49
ret_from_fork_asm+26
]: 65
热插拔
拔盘之后，系统都是咋运行的?
virtio queue 该如何上锁?
中断中回去修改 queue ，而且提交的时候也需要修改 queue ，所以 需要锁来控制
网络
在 __dev_queue_xmit 的第一个 rcu_read_lock_bh 下添加 lock ，那么可以看到
[ 71.272691] 4 locks held by NetworkManager/698:
[ 71.272733] #0: ffff0000c6444848 (sk_lock-AF_INET6){+.+.}-{0:0}, at: rawv6_sendmsg+0x664/0x14b0
[ 71.273094] #1: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip6_send_skb+0x34/0x230
[ 71.273133] #2: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip6_finish_output2+0x118/0xc58
[ 71.273171] #3: ffff800081558858 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x6c/0x1340
[ 73.327334] 4 locks held by sshd/1103:
[ 73.327371] #0: ffff0000c3240e48 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_sendmsg+0x30/0x70
[ 73.327464] #1: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: __ip_queue_xmit+0x8/0x858
[ 73.327522] #2: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0xfc/0x978
[ 73.327561] #3: ffff800081558858 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x6c/0x1340
[ 167.304430] 4 locks held by mount.nfs/1462:
[ 167.304501] #0: ffff0000c2a90248 (sk_lock-AF_INET-RPC){+.+.}-{0:0}, at: tcp_sock_set_cork+0x28/0x78
[ 167.304591] #1: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: __ip_queue_xmit+0x8/0x858
[ 167.304650] #2: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0xfc/0x978
[ 167.304729] #3: ffff800081558858 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x6c/0x1340
大致调用路径应该是这个样子的:
@[
__dev_queue_xmit+0
__ip_finish_output+176
ip_finish_output+60
ip_output+120
__ip_queue_xmit+432
ip_queue_xmit+28
__tcp_transmit_skb+1184
tcp_write_xmit+1152
tcp_push_one+68
tcp_sendmsg_locked+1384
tcp_sendmsg+64
inet_sendmsg+76
sock_write_iter+188
vfs_write+876
ksys_write+244
__arm64_sys_write+36
invoke_syscall.constprop.0+88
do_el0_svc+72
el0_svc+88
el0t_64_sync_handler+268
el0t_64_sync+408
]: 262183
唯一上的锁，言简意赅，就是一个 sock 只能同时被一个 thread 使用
int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
{
int ret;
lock_sock(sk);
ret = tcp_sendmsg_locked(sk, msg, size);
release_sock(sk);
return ret;
}
有时候感觉都是在滥用 rcu lock
[ 24.163867] 6 locks held by swapper/3/0:
[ 24.163960] #0: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: netif_receive_skb_list_internal+0xec/0x3f0
[ 24.164036] #1: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip_local_deliver_finish+0x60/0x1d0
[ 24.164102] #2: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: tcp_rcv_state_process+0x150/0x1128
[ 24.164163] #3: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: tcp_v4_send_synack+0xe8/0x3d0
[ 24.164224] #4: ffff800081558830 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0xfc/0x978
[ 24.164284] #5: ffff800081558858 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x6c/0x1340
真的有必要在 softirq 中嵌套这么多层的 rcu_read_lock 吗?
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