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Date:   Wed, 17 Oct 2018 18:30:01 -0700
From:   Joel Fernandes <joel@joelfernandes.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pstore: Refactor compression initialization
Message-ID: <20181018013001.GA99677@joelaf.mtv.corp.google.com>
References: <20181017214124.GA8239@beast>
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On Wed, Oct 17, 2018 at 02:41:24PM -0700, Kees Cook wrote:
> With compression initialization now separated from pstore_register(),
> there is no longer a good reason to do compression method selection
> during fs init. Instead, merge everything together into the late init.
> Additionally cleans up the reporting to be more clear.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> This patch goes on top of Joel's. I'll have both in linux-next shortly...
> ---
>  fs/pstore/inode.c    |  2 --
>  fs/pstore/internal.h |  3 --
>  fs/pstore/platform.c | 65 ++++++++++++++++++++++++++++----------------
>  3 files changed, 41 insertions(+), 29 deletions(-)
> 
> diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
> index 5fcb845b9fec..d814723fb27d 100644
> --- a/fs/pstore/inode.c
> +++ b/fs/pstore/inode.c
> @@ -486,8 +486,6 @@ static int __init init_pstore_fs(void)
>  {
>  	int err;
>  
> -	pstore_choose_compression();
> -
>  	/* Create a convenient mount point for people to access pstore */
>  	err = sysfs_create_mount_point(fs_kobj, "pstore");
>  	if (err)
> diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
> index fb767e28aeb2..c029314478fa 100644
> --- a/fs/pstore/internal.h
> +++ b/fs/pstore/internal.h
> @@ -37,7 +37,4 @@ extern bool	pstore_is_mounted(void);
>  extern void	pstore_record_init(struct pstore_record *record,
>  				   struct pstore_info *psi);
>  
> -/* Called during module_init() */
> -extern void __init pstore_choose_compression(void);
> -
>  #endif
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index f09066db2d4d..e4737a5fa68c 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -274,36 +274,56 @@ static int pstore_decompress(void *in, void *out,
>  
>  static void allocate_buf_for_compression(void)
>  {
> +	struct crypto_comp *ctx;
> +	int size;
> +	char *buf;
> +
> +	/* Skip if not built-in or compression backend not selected yet. */
>  	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS) || !zbackend)
>  		return;
>  
> +	/* Skip if no pstore backend yet or compression init already done. */
> +	if (!psinfo || tfm)
> +		return;
> +
>  	if (!crypto_has_comp(zbackend->name, 0, 0)) {
> -		pr_err("No %s compression\n", zbackend->name);
> +		pr_err("Unknown compression: %s\n", zbackend->name);
>  		return;
>  	}
>  
> -	big_oops_buf_sz = zbackend->zbufsize(psinfo->bufsize);
> -	if (big_oops_buf_sz <= 0)
> +	size = zbackend->zbufsize(psinfo->bufsize);
> +	if (size <= 0) {
> +		pr_err("Invalid compression size for %s: %d\n",
> +		       zbackend->name, size);
>  		return;
> +	}
>  
> -	big_oops_buf = kmalloc(big_oops_buf_sz, GFP_KERNEL);
> -	if (!big_oops_buf) {
> -		pr_err("allocate compression buffer error!\n");
> +	buf = kmalloc(size, GFP_KERNEL);
> +	if (!buf) {
> +		pr_err("Failed %d byte compression buffer allocation for: %s\n",
> +		       size, zbackend->name);
>  		return;
>  	}
>  
> -	tfm = crypto_alloc_comp(zbackend->name, 0, 0);
> -	if (IS_ERR_OR_NULL(tfm)) {
> -		kfree(big_oops_buf);
> -		big_oops_buf = NULL;
> -		pr_err("crypto_alloc_comp() failed!\n");
> +	ctx = crypto_alloc_comp(zbackend->name, 0, 0);
> +	if (IS_ERR_OR_NULL(ctx)) {
> +		kfree(buf);
> +		pr_err("crypto_alloc_comp('%s') failed: %ld\n", zbackend->name,
> +		       PTR_ERR(ctx));
>  		return;
>  	}
> +
> +	/* A non-NULL big_oops_buf indicates compression is available. */
> +	tfm = ctx;
> +	big_oops_buf_sz = size;
> +	big_oops_buf = buf;
> +
> +	pr_info("Using compression: %s\n", zbackend->name);
>  }
>  
>  static void free_buf_for_compression(void)
>  {
> -	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && !IS_ERR_OR_NULL(tfm))
> +	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm)
>  		crypto_free_comp(tfm);
>  	kfree(big_oops_buf);
>  	big_oops_buf = NULL;
> @@ -764,31 +784,28 @@ static void pstore_timefunc(struct timer_list *unused)
>  			  jiffies + msecs_to_jiffies(pstore_update_ms));
>  }
>  
> -void __init pstore_choose_compression(void)
> +static int __init pstore_compression_late_init(void)
>  {
>  	const struct pstore_zbackend *step;
>  
>  	if (!compress)
> -		return;
> +		return 0;
>  
> +	/* Locate desired compression method. */
>  	for (step = zbackends; step->name; step++) {
>  		if (!strcmp(compress, step->name)) {
>  			zbackend = step;
> -			pr_info("using %s compression\n", zbackend->name);
> -			return;
> +			break;
>  		}
>  	}
> -}
>  
> -static int __init pstore_compression_late_init(void)
> -{
>  	/*
> -	 * Check if any pstore backends registered earlier but did not allocate
> -	 * for compression because crypto was not ready, if so then initialize
> -	 * compression.
> +	 * Check if any pstore backends registered earlier but did not
> +	 * initialize compression because crypto was not ready. If so,
> +	 * then initialize compression now.
>  	 */
> -	if (psinfo && !tfm)
> -		allocate_buf_for_compression();
> +	allocate_buf_for_compression();

We can also get rid of the 'zbackend' global variable since choosing the
compression backend and allocating the buffers are done at the same time?

Otherwise looks good to me,

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>

thanks,

 - Joel