linux-kernel - Re: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates position index

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Message-ID: <20200508033625.GO16070@bombadil.infradead.org>
Date:   Thu, 7 May 2020 20:36:25 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vasily Averin <vvs@...tuozzo.com>, linux-kernel@...r.kernel.org,
        Waiman Long <longman@...hat.com>,
        Andreas Schwab <schwab@...e.de>
Subject: Re: [PATCH] ipc/util.c: sysvipc_find_ipc() incorrectly updates
 position index

On Thu, May 07, 2020 at 05:02:42PM -0700, Andrew Morton wrote:
> Here's how I resolved things.  Please check?
> 
> static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
> 					      loff_t *new_pos)
> {
> 	unsigned long index = pos;
> 	struct kern_ipc_perm *ipc;
> 
> 	rcu_read_lock();
> 	ipc = xa_find(&ids->ipcs, &index, ULONG_MAX, XA_PRESENT);
> 	if (ipc)
> 		ipc_lock_object(ipc);
> 	else
> 		rcu_read_unlock();
> 	*new_pos = pos + 1;
> 	return ipc;
> }

Surely that should be '*new_pos = index + 1'?  Or did I misunderstand
the reasoning behind the other patch?