linux-kernel - Re: [RFC/REFACT] Refactoring and significantly reducing code complexity

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Date:   Thu, 26 Oct 2023 09:45:18 +0800
From:   Wang Jinchao <wangjinchao@...sion.com>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
CC:     Steffen Klassert <steffen.klassert@...unet.com>,
        <linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stone.xulei@...sion.com>
Subject: Re: [RFC/REFACT] Refactoring and significantly reducing code
 complexity

On Thu, Oct 26, 2023 at 09:12:54AM +0800, Wang Jinchao wrote:
> On Wed, Oct 25, 2023 at 02:12:31PM -0400, Daniel Jordan wrote:
> > On Thu, Sep 28, 2023 at 04:53:38PM +0800, Wang Jinchao wrote:
> > > -/**
> > > - * struct parallel_data - Internal control structure, covers everything
> > > - * that depends on the cpumask in use.
> > > - *
> > > - * @ps: padata_shell object.
> > > - * @reorder_list: percpu reorder lists
> > > - * @squeue: percpu padata queues used for serialuzation.
> > > - * @refcnt: Number of objects holding a reference on this parallel_data.
> > > - * @seq_nr: Sequence number of the parallelized data object.
> > > - * @processed: Number of already processed objects.
> > > - * @cpu: Next CPU to be processed.
> > > - * @cpumask: The cpumasks in use for parallel and serial workers.
> > > - * @reorder_work: work struct for reordering.
> > > - * @lock: Reorder lock.
> > > - */
> > > -struct parallel_data {
> > > -	struct padata_shell		*ps;
> > > -	struct padata_list		__percpu *reorder_list;
> > > -	struct padata_serial_queue	__percpu *squeue;
> > > -	refcount_t			refcnt;
> > > -	unsigned int			seq_nr;
> > > -	unsigned int			processed;
> > > -	int				cpu;
> > > -	struct padata_cpumask		cpumask;
> > > -	struct work_struct		reorder_work;
> > > -	spinlock_t                      ____cacheline_aligned lock;
> > > -};
> > 
> > reorder_list used to serialize one sequence of objects per padata_shell,
> > but now serial_wq serializes all sequences of objects in one list of
> > work_structs.  That works in theory, since a total order can maintain
> > each sequence's order, but it's possible (not sure yet, need to think
> > more) that this could lead to deadlocks or other issues in odd cases
> > such as the one that padata_shell was introduced for in bbefa1dd6a6d
> > ("crypto: pcrypt - Avoid deadlock by using per-instance padata queues").
> > 
> Yes, you are correct. This version is not only ordered at the padata_shell
> level but at the instance level, which indeed doesn't align with the design.
> Apart from potential deadlocks, it may also cause a padata_shell_B that
> should have completed earlier to be blocked by an unrelated padata_shell_B.
> I will address this issue in subsequent patches.
Apart from potential deadlocks, it may also cause a padata_shell_B that
should have completed earlier to be blocked by an unrelated padata_shell_A.
I will address this issue in subsequent patches.