From: Amir Goldstein <amir73il@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>, Jan Kara <jack@suse.cz>
Subject: Re: [bug report] fsnotify: pass dir and inode arguments to fsnotify()
Date: Thu, 30 Jul 2020 14:55:11 +0300 [thread overview]
Message-ID: <CAOQ4uxgEG9PNtdoMXw52_C4oaUQpi2DVx34_QEHeV195e3kYdg@mail.gmail.com> (raw)
In-Reply-To: <20200730111339.GA54272@mwanda>
On Thu, Jul 30, 2020 at 2:13 PM <dan.carpenter@oracle.com> wrote:
>
> Hello Amir Goldstein,
>
> This is a semi-automatic email about new static checker warnings.
>
> The patch 40a100d3adc1: "fsnotify: pass dir and inode arguments to
> fsnotify()" from Jul 22, 2020, leads to the following Smatch
> complaint:
That's an odd report, because...
>
> fs/notify/fsnotify.c:460 fsnotify()
> warn: variable dereferenced before check 'inode' (see line 449)
>
> fs/notify/fsnotify.c
> 448 }
> 449 sb = inode->i_sb;
> ^^^^^^^^^^^
> New dreference.
First of all, two lines above we have
if (!inode) inode = dir;
This function does not assert (inode || dir), but must it??
This is even documented:
* @inode: optional inode associated with event -
* either @dir or @inode must be non-NULL.
Second,
The line above was indeed added by:
40a100d3adc1: "fsnotify: pass dir and inode arguments to fsnotify()"
However...
>
> 450
> 451 /*
> 452 * Optimization: srcu_read_lock() has a memory barrier which can
> 453 * be expensive. It protects walking the *_fsnotify_marks lists.
> 454 * However, if we do not walk the lists, we do not have to do
> 455 * SRCU because we have no references to any objects and do not
> 456 * need SRCU to keep them "alive".
> 457 */
> 458 if (!sb->s_fsnotify_marks &&
> 459 (!mnt || !mnt->mnt_fsnotify_marks) &&
> 460 (!inode || !inode->i_fsnotify_marks) &&
> ^^^^^^
> Check too late. Presumably this check can be removed?
But this line was only added later by:
9b93f33105f5 fsnotify: send event with parent/name info to
sb/mount/non-dir marks
So, yes, the check could be removed.
It is a leftover from a previous revision, but even though it is a leftover
I kind of like the code better this way.
In principle, an event on sb/mnt that is not associated with any inode
(for example
FS_UNMOUNT) could be added in the future.
And then we will have to fix documentation and the inode dereference above.
In any case, thank you for the report, but I don't see a reason to make any
changes right now.
Thanks,
Amir.
next prev parent reply other threads:[~2020-07-30 11:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 11:13 [bug report] fsnotify: pass dir and inode arguments to fsnotify() dan.carpenter
2020-07-30 11:55 ` Amir Goldstein [this message]
2020-07-30 19:25 ` Jan Kara
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=CAOQ4uxgEG9PNtdoMXw52_C4oaUQpi2DVx34_QEHeV195e3kYdg@mail.gmail.com \
--to=amir73il@gmail.com \
--cc=dan.carpenter@oracle.com \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
/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).