linux-kernel - Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram

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Date:   Tue, 30 Oct 2018 14:38:18 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peng Wang <wangpeng15@...omi.com>
Cc:     keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, linux-kernel@...r.kernel.org,
        vipwangerxiao@...il.com
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()

On Tue, Oct 30, 2018 at 03:52:34PM +0800, Peng Wang wrote:
> When initialing prz with invalid data in buffer(no PERSISTENT_RAM_SIG),
> function call path is like this:
> 
> ramoops_init_prz ->
> |
> |-> persistent_ram_new -> persistent_ram_post_init -> persistent_ram_zap
> |
> |-> persistent_ram_zap
> 
> As we can see, persistent_ram_zap() is called twice.
> We can avoid this by adding an option to persistent_ram_new(), and
> only call persistent_ram_zap() when it is needed.
> 
> Signed-off-by: Peng Wang <wangpeng15@...omi.com>
> ---
>  fs/pstore/ram.c            | 4 +---
>  fs/pstore/ram_core.c       | 5 +++--
>  include/linux/pstore_ram.h | 1 +
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index ffcff6516e89..b51901f97dc2 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -640,7 +640,7 @@ static int ramoops_init_prz(const char *name,
>  
>  	label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
>  	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
> -				  cxt->memtype, 0, label);
> +				  cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
>  	if (IS_ERR(*prz)) {
>  		int err = PTR_ERR(*prz);

Looks good to me except the minor comment below:

>  
> @@ -649,8 +649,6 @@ static int ramoops_init_prz(const char *name,
>  		return err;
>  	}
>  
> -	persistent_ram_zap(*prz);
> -
>  	*paddr += sz;
>  
>  	return 0;
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index 12e21f789194..2ededd1ea1c2 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -505,15 +505,16 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
>  			pr_debug("found existing buffer, size %zu, start %zu\n",
>  				 buffer_size(prz), buffer_start(prz));
>  			persistent_ram_save_old(prz);
> -			return 0;
> +			if (!(prz->flags & PRZ_FLAG_ZAP_OLD))
> +				return 0;

This could be written differently.

We could just do:

if (prz->flags & PRZ_FLAG_ZAP_OLD)
	persistent_ram_zap(prz);

And remove the zap from below below.

Since Kees already took this patch, I can just patch this in my series if
Kees and you are Ok with this suggestion.

Sorry for the delay in my RFC series, I just got back from paternity leave
and I'm catching up with email.

thanks,

- Joel

>  		}
>  	} else {
>  		pr_debug("no valid data in buffer (sig = 0x%08x)\n",
>  			 prz->buffer->sig);
> +		prz->buffer->sig = sig;
>  	}
>  
>  	/* Rewind missing or invalid memory area. */
> -	prz->buffer->sig = sig;
>  	persistent_ram_zap(prz);
>  
>  	return 0;