linux-kernel - Re: [PATCH] 9p: Avoid creating multiple slab caches with the same name

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Message-ID: <Zxa0K-4mhSI91S-w@telecaster.dhcp.thefacebook.com>
Date: Mon, 21 Oct 2024 13:06:03 -0700
From: Omar Sandoval <osandov@...ndov.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Vlastimil Babka <vbabka@...e.cz>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Thorsten Leemhuis <regressions@...mhuis.info>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Christian Schoenebeck <linux_oss@...debyte.com>,
	v9fs@...ts.linux.dev, linux-kernel@...r.kernel.org,
	regressions@...ts.linux.dev, Jason Gunthorpe <jgg@...dia.com>,
	Pedro Falcato <pedro.falcato@...il.com>
Subject: Re: [PATCH] 9p: Avoid creating multiple slab caches with the same
 name

On Mon, Oct 21, 2024 at 11:57:38AM -0700, Linus Torvalds wrote:
> On Mon, 21 Oct 2024 at 11:37, Omar Sandoval <osandov@...ndov.com> wrote:
> >
> > FYI, drgn's CI started getting EIO errors from
> > getdents("/sys/kernel/slab") that I bisected to this patch. The problem
> > is that dev_name can be an arbitrary string. In my case, it is
> > "/dev/root". This trips verify_dirent_name(), which fails if a filename
> > contains a slash.
> 
> Bah. Does something silly like this fix it:
> 
>   --- a/net/9p/client.c
>   +++ b/net/9p/client.c
>   @@ -977,6 +977,7 @@ static int p9_client_version(struct p9_client *c)
>    struct p9_client *p9_client_create(const char *dev_name, char *options)
>    {
>         int err;
>   +     static atomic_t seqno = ATOMIC_INIT(0);
>         struct p9_client *clnt;
>         char *client_id;
>         char *cache_name;
>   @@ -1036,7 +1037,8 @@ struct p9_client *p9_client_create(const char
> *dev_name, char *options)
>         if (err)
>                 goto close_trans;
> 
>   -     cache_name = kasprintf(GFP_KERNEL, "9p-fcall-cache-%s", dev_name);
>   +     cache_name = kasprintf(GFP_KERNEL,
>   +             "9p-fcall-cache-%d", atomic_inc_return(&seqno));
>         if (!cache_name) {
>                 err = -ENOMEM;
>                 goto close_trans;
> 
> (whitespace-damaged, but you get the idea)

Yup, that works here.

Tested-by: Omar Sandoval <osandov@...com>