From: Al Viro <viro@zeniv.linux.org.uk>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Gao Xiang <hsiangkao@aol.com>,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
Daniel Rosenberg <drosen@google.com>,
Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash()
Date: Fri, 24 Jan 2020 18:31:03 +0000 [thread overview]
Message-ID: <20200124183103.GJ23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200124181253.GA41762@gmail.com>
On Fri, Jan 24, 2020 at 10:12:54AM -0800, Eric Biggers wrote:
> > Thanks for your web reference, I will look into it. I think there
> > is no worry about dentry->d_parent here because of this only one
> > dereference on dentry->d_parent.
> >
> > You could ignore my words anyway, just my little thought though.
> > Other part of the patch is ok.
> >
>
> While that does make it really unlikely to cause a real-world problem, it's
> still undefined behavior to not properly annotate a data race, it would make the
> code harder to understand as there would be no indication that there's a data
> race, and it would confuse tools that try to automatically detect data races.
> So let's keep the READ_ONCE() on d_parent.
*nod*
Note that on everything except alpha it'll generate the same code, unless
the compiler screws up an generates multiple loads. On alpha it adds
a barrier and I really don't want to sit down and check if its absense
could lead to anything unpleasant.
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@zeniv.linux.org.uk>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Daniel Rosenberg <drosen@google.com>,
Gao Xiang <hsiangkao@aol.com>,
linux-f2fs-devel@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [f2fs-dev] [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash()
Date: Fri, 24 Jan 2020 18:31:03 +0000 [thread overview]
Message-ID: <20200124183103.GJ23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200124181253.GA41762@gmail.com>
On Fri, Jan 24, 2020 at 10:12:54AM -0800, Eric Biggers wrote:
> > Thanks for your web reference, I will look into it. I think there
> > is no worry about dentry->d_parent here because of this only one
> > dereference on dentry->d_parent.
> >
> > You could ignore my words anyway, just my little thought though.
> > Other part of the patch is ok.
> >
>
> While that does make it really unlikely to cause a real-world problem, it's
> still undefined behavior to not properly annotate a data race, it would make the
> code harder to understand as there would be no indication that there's a data
> race, and it would confuse tools that try to automatically detect data races.
> So let's keep the READ_ONCE() on d_parent.
*nod*
Note that on everything except alpha it'll generate the same code, unless
the compiler screws up an generates multiple loads. On alpha it adds
a barrier and I really don't want to sit down and check if its absense
could lead to anything unpleasant.
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Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
next prev parent reply other threads:[~2020-01-24 18:31 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-24 4:12 [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Eric Biggers
2020-01-24 4:12 ` [f2fs-dev] " Eric Biggers
2020-01-24 5:04 ` Gao Xiang
2020-01-24 5:04 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel
2020-01-24 5:16 ` Eric Biggers
2020-01-24 5:16 ` [f2fs-dev] " Eric Biggers
2020-01-24 5:27 ` Gao Xiang
2020-01-24 5:27 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel
2020-01-24 5:53 ` Eric Biggers
2020-01-24 5:53 ` [f2fs-dev] " Eric Biggers
2020-01-24 5:34 ` Gao Xiang
2020-01-24 5:34 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel
2020-01-24 5:42 ` Eric Biggers
2020-01-24 5:42 ` [f2fs-dev] " Eric Biggers
2020-01-24 6:15 ` Gao Xiang
2020-01-24 6:15 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel
2020-01-24 18:12 ` Eric Biggers
2020-01-24 18:12 ` [f2fs-dev] " Eric Biggers
2020-01-24 18:31 ` Al Viro [this message]
2020-01-24 18:31 ` Al Viro
2020-01-25 3:35 ` Theodore Y. Ts'o
2020-01-25 3:35 ` [f2fs-dev] " Theodore Y. Ts'o
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