Re: [PATCH v1 4/5] misc: fastrpc: Remove buffer from list prior to unmap operation

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 5/19/2025 3:50 PM, Dmitry Baryshkov wrote:
> On Tue, May 13, 2025 at 09:58:24AM +0530, Ekansh Gupta wrote:
>> fastrpc_req_munmap_impl() is called to unmap any buffer. The buffer is
>> getting removed from the list after it is unmapped from DSP. This can
>> create potential race conditions if any other thread removes the entry
>> from list while unmap operation is ongoing. Remove the entry before
>> calling unmap operation.
>>
>> Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
>> Cc: stable@kernel.org
>> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
>> ---
>>  drivers/misc/fastrpc.c | 29 ++++++++++++++++++++++-------
>>  1 file changed, 22 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index b629e24f00bc..d54368bf8c5c 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -1868,9 +1868,6 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl, struct fastrpc_buf *
>>  				      &args[0]);
>>  	if (!err) {
>>  		dev_dbg(dev, "unmmap\tpt 0x%09lx OK\n", buf->raddr);
>> -		spin_lock(&fl->lock);
>> -		list_del(&buf->node);
>> -		spin_unlock(&fl->lock);
>>  		fastrpc_buf_free(buf);
>>  	} else {
>>  		dev_err(dev, "unmmap\tpt 0x%09lx ERROR\n", buf->raddr);
>> @@ -1884,13 +1881,15 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>>  	struct fastrpc_buf *buf = NULL, *iter, *b;
>>  	struct fastrpc_req_munmap req;
>>  	struct device *dev = fl->sctx->dev;
>> +	int err;
>>  
>>  	if (copy_from_user(&req, argp, sizeof(req)))
>>  		return -EFAULT;
>>  
>>  	spin_lock(&fl->lock);
>>  	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
>> -		if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
>> +		if (iter->raddr == req.vaddrout && iter->size == req.size) {
> Cosmetics, please drop.
Ack.
>
>> +			list_del(&iter->node);
>>  			buf = iter;
>>  			break;
>>  		}
>> @@ -1903,7 +1902,14 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>>  		return -EINVAL;
>>  	}
>>  
>> -	return fastrpc_req_munmap_impl(fl, buf);
>> +	err = fastrpc_req_munmap_impl(fl, buf);
>> +	if (err) {
>> +		spin_lock(&fl->lock);
>> +		list_add_tail(&buf->node, &fl->mmaps);
>> +		spin_unlock(&fl->lock);
>> +	}
>> +
>> +	return err;
>>  }
>>  
>>  static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
>> @@ -1997,14 +2003,23 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
>>  
>>  	if (copy_to_user((void __user *)argp, &req, sizeof(req))) {
>>  		err = -EFAULT;
>> -		goto err_assign;
>> +		goto err_copy;
>>  	}
>>  
>>  	dev_dbg(dev, "mmap\t\tpt 0x%09lx OK [len 0x%08llx]\n",
>>  		buf->raddr, buf->size);
>>  
>>  	return 0;
>> -
> Please keep the empty line here, it improves readability.
Ack.
>
>> +err_copy:
>> +	if (req.flags == ADSP_MMAP_REMOTE_HEAP_ADDR) {
>> +		spin_lock_irqsave(&fl->cctx->lock, flags);
>> +		list_del(&buf->node);
>> +		spin_unlock_irqrestore(&fl->cctx->lock, flags);
>> +	} else {
>> +		spin_lock(&fl->lock);
>> +		list_del(&buf->node);
>> +		spin_unlock(&fl->lock);
>> +	}
> Can we store the spinlock pointer in the struct fastrpc_buf instead?
this spinlock is used for multiple lists(bufs, maps and ctx).
>
>>  err_assign:
>>  	fastrpc_req_munmap_impl(fl, buf);
>>  
>> -- 
>> 2.34.1
>>