linux-kernel - Re: [PATCH] nfp: nfp_alloc

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Message-ID: <CAC1kPDNE+io5=KEXZkLq5DOQi2qzBEmgAwOj6x4qvhiNmC1rtQ@mail.gmail.com>
Date: Tue, 1 Jul 2025 15:54:57 +0800
From: Chen Linxuan <chenlinxuan@...ontech.com>
To: Chen Linxuan <chenlinxuan@...ontech.com>
Cc: Jakub Kicinski <kuba@...nel.org>, WangYuli <wangyuli@...ontech.com>, louis.peens@...igine.com, 
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, 
	pabeni@...hat.com, viro@...iv.linux.org.uk, oss-drivers@...igine.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	guanwentao@...ontech.com, niecheng1@...ontech.com, 
	Jun Zhan <zhanjun@...ontech.com>
Subject: Re: [PATCH] nfp: nfp_alloc_bar: Fix double unlock

On Tue, Jul 1, 2025 at 3:45 PM Chen Linxuan <chenlinxuan@...ontech.com> wrote:
>
> On Tue, Jun 24, 2025 at 4:12 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Mon, 23 Jun 2025 12:11:04 +0800 WangYuli wrote:
> > > The lock management in the nfp_alloc_bar function is problematic:
> > >
> > >  *1. The function acquires the lock at the beginning:
> > > spin_lock_irqsave(&nfp->bar_lock, irqflags).
> > >
> > >   2. When barnum < 0 and in non-blocking mode, the code jumps to
> > > the err_nobar label. However, in this non-blocking path, if
> > > barnum < 0, the code releases the lock and calls nfp_wait_for_bar.
> > >
> > >   3. Inside nfp_wait_for_bar, find_unused_bar_and_lock is called,
> > > which holds the lock upon success (indicated by the __release
> > > annotation). Consequently, when nfp_wait_for_bar returns
> > > successfully, the lock is still held.
> > >
> > >   4. But at the err_nobar label, the code always executes
> > > spin_unlock_irqrestore(&nfp->bar_lock, irqflags).
> > >
> > >   5. The problem arises when nfp_wait_for_bar successfully finds a
> > > BAR: the lock is still held, but if a subsequent reconfigure_bar
> > > fails, the code will attempt to unlock it again at err_nobar,
> > > leading to a double unlock.
> >
> > I don't understand what you're trying to say.
> > If you think your analysis is correct please provide a more exact
> > execution path with a code listing.
>
> In nfp_alloc_bar(), if
>
> - find_matching_bar() fails to find a bar
> - find_unused_bar_noblock also fails to find a bar
> - nonblocking == false
> - nfp_wait_for_bar returns 0
>
> In this situation, when executing nfp_bar_get(nfp, &nfp->bar[barnum]),
> the code does not hold &nfp->bar_lock.
> We referred to similar logic in other drivers:
> https://elixir.bootlin.com/linux/v6.13/source/sound/usb/line6/driver.c#L565
> It seems that a lock should be acquired here again.

Sorry, I found that find_unused_bar_and_lock already re-locks it. I
didn't notice it before. Please ignore the entire thread.

>
> > --
> > pw-bot: cr
> >
> >