Re: [PATCH] blk-iocost: use irq-safe locking in cgroup handlers

[Yu Kuai]

Hi,

在 2026/6/2 5:50, Bart Van Assche 写道:
> On 5/31/26 11:13 PM, Yu Kuai wrote:
>> @@ -3378,14 +3378,14 @@ static u64 ioc_cost_model_prfill(struct 
>> seq_file *sf,
>>       if (!dname)
>>           return 0;
>>   -    spin_lock(&ioc->lock);
>> +    spin_lock_irq(&ioc->lock);
>>       seq_printf(sf, "%s ctrl=%s model=linear "
>>              "rbps=%llu rseqiops=%llu rrandiops=%llu "
>>              "wbps=%llu wseqiops=%llu wrandiops=%llu\n",
>>              dname, ioc->user_cost_model ? "user" : "auto",
>>              u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS],
>>              u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], 
>> u[I_LCOEF_WRANDIOPS]);
>> -    spin_unlock(&ioc->lock);
>> +    spin_unlock_irq(&ioc->lock);
>>       return 0;
>>   }
>
> This change is wrong. ioc_cost_model_prfill() only has one caller,
> namely blkcg_print_blkgs(). blkcg_print_blkgs() calls the above function
> with interrupts disabled. The spin_unlock_irq(&ioc->lock) at the end of
> the above function enables interrupts while q->queue_lock is held. If an
> interrupt happens on the same CPU core before q->queue_lock is unlocked,
> and that interrupt tries to lock q->queue_lock, a deadlock will occur.

Yes, this is correct. Sorry I just notice this is a sysfs api like other
places and didn't notice the problem. So ioc_weight_write() is the only
place that need the fix.

Jens, please let me not if you want me to send a v2 or a fix.

>
> Bart.

-- 
Thansk,
Kuai