linux-kernel - Re: [PATCH] lightnvm: pblk: Fix two sleep-in-atomic-context bugs in pblk_line_submit_smeta

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Date:   Tue, 4 Sep 2018 17:52:20 +0000
From:   Javier Gonzalez <javier@...xlabs.com>
To:     Matias Bjørling <mb@...htnvm.io>
CC:     "baijiaju1990@...il.com" <baijiaju1990@...il.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hans Holmberg <hans.holmberg@...xlabs.com>
Subject: Re: [PATCH] lightnvm: pblk: Fix two sleep-in-atomic-context bugs in
 pblk_line_submit_smeta_io()

> On 4 Sep 2018, at 03.11, Matias Bjørling <mb@...htnvm.io> wrote:
> 
> On 09/01/2018 01:53 PM, Jia-Ju Bai wrote:
>> The driver may sleep with holding a spinlock.
>> The function call paths (from bottom to top) in Linux-4.16 are:
>> [FUNC] nvm_dev_dma_alloc(GFP_KERNEL)
>> drivers/lightnvm/pblk-core.c, 754:
>> 	nvm_dev_dma_alloc in pblk_line_submit_smeta_io
>> drivers/lightnvm/pblk-core.c, 1048:
>> 	pblk_line_submit_smeta_io in pblk_line_init_bb
>> drivers/lightnvm/pblk-core.c, 1434:
>> 	pblk_line_init_bb in pblk_line_replace_data
>> drivers/lightnvm/pblk-recovery.c, 980:
>> 	pblk_line_replace_data in pblk_recov_l2p
>> drivers/lightnvm/pblk-recovery.c, 976:
>> 	spin_lock in pblk_recov_l2p
>> [FUNC] bio_map_kern(GFP_KERNEL)
>> drivers/lightnvm/pblk-core.c, 762:
>> 	bio_map_kern in pblk_line_submit_smeta_io
>> drivers/lightnvm/pblk-core.c, 1048:
>> 	pblk_line_submit_smeta_io in pblk_line_init_bb
>> drivers/lightnvm/pblk-core.c, 1434:
>> 	pblk_line_init_bb in pblk_line_replace_data
>> drivers/lightnvm/pblk-recovery.c, 980:
>> 	pblk_line_replace_data in pblk_recov_l2p
>> drivers/lightnvm/pblk-recovery.c, 976:
>> 	spin_lock in pblk_recov_l2p
>> To fix these bugs, GFP_KERNEL is replaced with GFP_ATOMIC.
>> These bugs are found by my static analysis tool DSAC.
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> ---
>>  drivers/lightnvm/pblk-core.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
>> index ed9cc977c8b3..5d915c93b6cf 100644
>> --- a/drivers/lightnvm/pblk-core.c
>> +++ b/drivers/lightnvm/pblk-core.c
>> @@ -802,7 +802,7 @@ static int pblk_line_submit_smeta_io(struct pblk *pblk, struct pblk_line *line,
>>    	memset(&rqd, 0, sizeof(struct nvm_rq));
>>  -	rqd.meta_list = nvm_dev_dma_alloc(dev->parent, GFP_KERNEL,
>> +	rqd.meta_list = nvm_dev_dma_alloc(dev->parent, GFP_ATOMIC,
>>  							&rqd.dma_meta_list);
>>  	if (!rqd.meta_list)
>>  		return -ENOMEM;
>> @@ -810,7 +810,7 @@ static int pblk_line_submit_smeta_io(struct pblk *pblk, struct pblk_line *line,
>>  	rqd.ppa_list = rqd.meta_list + pblk_dma_meta_size;
>>  	rqd.dma_ppa_list = rqd.dma_meta_list + pblk_dma_meta_size;
>>  -	bio = bio_map_kern(dev->q, line->smeta, lm->smeta_len, GFP_KERNEL);
>> +	bio = bio_map_kern(dev->q, line->smeta, lm->smeta_len, GFP_ATOMIC);
>>  	if (IS_ERR(bio)) {
>>  		ret = PTR_ERR(bio);
>>  		goto free_ppa_list;
> 
> Javier,
> 
> What do you think? I'm OK with applying this, but one could also move
> the allocs outside the spinlocks?
> 

Definitely better to take the allocation out of the spin_lock(), as all
line preparations are made to be lock free.

It is fairly simple to fix this, as it only occurs when calling
pblk_line_replace_data() from pblk_recov_l2p(). Here the lock can be
inside the if statement to only cover text_and_clear_bit() and to the
else statement to cover it entirely.

 Jia-Ju Bai: Do you want to send a patch for this?

Javier


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