linux-kernel - Re: [PATCH 1/2] fs: avoid fdput() after failed fdget() in ksys_sync_file

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Message-ID: <20200508002422.GL23230@ZenIV.linux.org.uk>
Date:   Fri, 8 May 2020 01:24:22 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     axboe@...nel.dk, zohar@...ux.vnet.ibm.com, mcgrof@...nel.org,
        keescook@...omium.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: avoid fdput() after failed fdget() in
 ksys_sync_file_range()

On Fri, May 08, 2020 at 01:05:09AM +0100, Al Viro wrote:
> On Thu, May 07, 2020 at 05:57:09PM -0600, Shuah Khan wrote:
> > Fix ksys_sync_file_range() to avoid fdput() after a failed fdget().
> > fdput() doesn't do fput() on this file since FDPUT_FPUT isn't set
> > in fd.flags. Fix it anyway since failed fdget() doesn't require
> > a fdput().
> > 
> > This was introdcued in a commit to add sync_file_range() helper.
> 
> Er...  What's the point microoptimizing the slow path here?

PS: I'm not saying the patch is incorrect, but Fixes: is IMO over the
top.  And looking at that thing,
{
        struct fd f = fdget(fd);
        int ret;

	if (unlikely(!f.file))
		return -EBADF;

	ret = sync_file_range(f.file, offset, nbytes, flags);
        fdput(f);
        return ret;
}

might be cleaner, but that's a matter of taste...