linux-kernel - Re: [PATCH v26 07/13] mm/damon: Implement a debugfs-based user space interface

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Date:   Tue, 30 Mar 2021 10:20:06 +0000
From:   SeongJae Park <sj38.park@...il.com>
To:     SeongJae Park <sj38.park@...il.com>
Cc:     Greg KH <greg@...ah.com>, akpm@...ux-foundation.org,
        SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        amit@...nel.org, benh@...nel.crashing.org,
        brendanhiggins@...gle.com, corbet@....net, david@...hat.com,
        dwmw@...zon.com, elver@...gle.com, fan.du@...el.com,
        foersleo@...zon.de, gthelen@...gle.com, guoju.fgj@...baba-inc.com,
        mgorman@...e.de, minchan@...nel.org, mingo@...hat.com,
        namhyung@...nel.org, peterz@...radead.org, riel@...riel.com,
        rientjes@...gle.com, rostedt@...dmis.org, rppt@...nel.org,
        shakeelb@...gle.com, shuah@...nel.org, snu@...zon.de,
        vbabka@...e.cz, vdavydov.dev@...il.com, zgf574564920@...il.com,
        linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v26 07/13] mm/damon: Implement a debugfs-based user space interface

From: SeongJae Park <sjpark@...zon.de>

On Tue, 30 Mar 2021 09:59:50 +0000 SeongJae Park <sj38.park@...il.com> wrote:

> From: SeongJae Park <sjpark@...zon.de>
> 
> On Tue, 30 Mar 2021 11:22:45 +0200 Greg KH <greg@...ah.com> wrote:
> 
> > On Tue, Mar 30, 2021 at 09:05:31AM +0000, sj38.park@...il.com wrote:
> > > +static int __init __damon_dbgfs_init(void)
> > > +{
> > > +	struct dentry *dbgfs_root;
> > > +	const char * const file_names[] = {"monitor_on"};
> > > +	const struct file_operations *fops[] = {&monitor_on_fops};
> > > +	int i;
> > > +
> > > +	dbgfs_root = debugfs_create_dir("damon", NULL);
> > > +
> > > +	for (i = 0; i < ARRAY_SIZE(file_names); i++)
> > > +		debugfs_create_file(file_names[i], 0600, dbgfs_root, NULL,
> > > +				fops[i]);
> > > +	dbgfs_fill_ctx_dir(dbgfs_root, dbgfs_ctxs[0]);
> > > +
> > > +	dbgfs_dirs = kmalloc_array(1, sizeof(dbgfs_root), GFP_KERNEL);
> > 
> > No error checking for memory allocation failures?
> 
> Oops, I will add the check in the next spin.
> 
> > 
> > 
> > > +	dbgfs_dirs[0] = dbgfs_root;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +/*
> > > + * Functions for the initialization
> > > + */
> > > +
> > > +static int __init damon_dbgfs_init(void)
> > > +{
> > > +	int rc;
> > > +
> > > +	dbgfs_ctxs = kmalloc(sizeof(*dbgfs_ctxs), GFP_KERNEL);
> > 
> > No error checking?
> 
> Will add in the next spin.
> 
> > 
> > > +	dbgfs_ctxs[0] = dbgfs_new_ctx();
> > > +	if (!dbgfs_ctxs[0])
> > > +		return -ENOMEM;

And, I found that I'm not printing the error for this failure.  I guess this
might made you to to think below error message should printed inside the
callee.

I will add 'pr_err()' here and above unchecked failure case, in the next
version.

BTW, I forgot saying thank you for your review.  Appreciate!


Thanks,
SeongJae Park

> > > +	dbgfs_nr_ctxs = 1;
> > > +
> > > +	rc = __damon_dbgfs_init();
> > > +	if (rc)
> > > +		pr_err("%s: dbgfs init failed\n", __func__);
> > 
> > Shouldn't the error be printed out in the function that failed, not in
> > this one?
> 
> I thought some other functions (in future) might want to use
> '__damon_dbgfs_init()' but siletnly handles it's failure.  Therefore I made the
> function fails silently but returns the error code explicitly.  Am I missing
> somthing?
> 
> 
> Thanks,
> SeongJae Park
> 
> > 
> > thanks,
> > 
> > greg k-h
>