linux-kernel - Re: [PATCH] ubifs: Remove a redundant null check on pointer lp

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Date:   Tue, 22 Jun 2021 09:24:15 +0200 (CEST)
From:   Richard Weinberger <richard@....at>
To:     chengzhihao1 <chengzhihao1@...wei.com>
Cc:     Colin Ian King <colin.king@...onical.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ubifs: Remove a redundant null check on pointer lp

----- Ursprüngliche Mail -----
> I just found out about it today thanks to your patch. Commit
> c770cd5190ba ("ubifs: fix an IS_ERR() vs NULL check") did import a new
> problem that ubifs_gc_start_commit() may return -ENOMEM while syncing fs.
> I guess ubifs_fast_find_frdi_idx() return NULL pointer is the
> termination condition in while-loop, which means we cannot get a
> freeable index LEB in ubifs_gc_start_commit().

Good catch! :-)

>> -		if (!lp)
>> -			break;
>>   		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
>>   		if (!idx_gc) {
>>   			err = -ENOMEM;
>> 
> BTW, the following modifications may be what you want?
> diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
> index 7cc22d7317ea..b1f276599b04 100644
> --- a/fs/ubifs/gc.c
> +++ b/fs/ubifs/gc.c
> @@ -895,10 +895,6 @@ int ubifs_gc_start_commit(struct ubifs_info *c)
>         /* Record index freeable LEBs for unmapping after commit */
>         while (1) {
>                 lp = ubifs_fast_find_frdi_idx(c);
> -               if (!lp) {
> -                       err = -ENOMEM;
> -                       goto out;
> -               }
>                 if (!lp)
>                         break;
>                 idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb),
> GFP_NOFS);

I'll drop Dan's patch from -next. Do you want to send a followup patch which removes the
in vain check?

Thanks,
//richard