linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [tracepoint] cargo-culting considered harmful...
Date: Wed, 23 Jan 2013 15:51:47 -0800	[thread overview]
Message-ID: <20130123155147.25fe49a2.akpm@linux-foundation.org> (raw)
In-Reply-To: <20130123225523.GY4939@ZenIV.linux.org.uk>

On Wed, 23 Jan 2013 22:55:24 +0000
Al Viro <viro@ZenIV.linux.org.uk> wrote:

> In samples/tracepoints/tracepoint-probe-sample.c:
> /*
>  * Here the caller only guarantees locking for struct file and struct inode.
>  * Locking must therefore be done in the probe to use the dentry.
>  */
> static void probe_subsys_event(void *ignore,   
>                                struct inode *inode, struct file *file)
> {
>         path_get(&file->f_path);
>         dget(file->f_path.dentry);
>         printk(KERN_INFO "Event is encountered with filename %s\n",
>                 file->f_path.dentry->d_name.name);
>         dput(file->f_path.dentry);
>         path_put(&file->f_path);
> }
> 
> note that
> 	* file->f_path is already pinned down by open(), path_get() does not
> provide anything extra.
> 	* file->f_path.dentry is already pinned by open() *and* path_get()
> just above that dget().
> 	* ->d_name.name *IS* *NOT* *PROTECTED* by pinning dentry down,
> whether it's done once or thrice.

I guess the first two are obvious (or at least, expected).  But the
third isn't.

Where should a kernel developer go to learn these things? 
include/linux/dcache.h doesn't mention d_name locking rules, nor does
Documentation/filesystems/vfs.txt.


  parent reply	other threads:[~2013-01-23 23:52 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-23 22:55 [tracepoint] cargo-culting considered harmful Al Viro
2013-01-23 23:02 ` Steven Rostedt
2013-01-25 14:38   ` Mathieu Desnoyers
2013-01-25 15:27     ` Steven Rostedt
2013-01-25 16:14       ` Mathieu Desnoyers
2013-01-23 23:51 ` Andrew Morton [this message]
2013-01-24  1:48   ` Al Viro
2013-01-25 14:49     ` Mathieu Desnoyers
2013-01-25 15:32       ` Al Viro
2013-01-25 17:30         ` Mathieu Desnoyers
2013-02-03 19:16 ` [tip:perf/core] tracing: Remove tracepoint sample code tip-bot for Steven Rostedt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20130123155147.25fe49a2.akpm@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@polymtl.ca \
    --cc=torvalds@linux-foundation.org \
    --cc=viro@ZenIV.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).