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

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Message-ID: <20250623131141.332c631c@kernel.org>
Date: Mon, 23 Jun 2025 13:11:41 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: WangYuli <wangyuli@...ontech.com>
Cc: louis.peens@...igine.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, pabeni@...hat.com, chenlinxuan@...ontech.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 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.
-- 
pw-bot: cr