linux-kernel - Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty

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Message-ID: <87r4cc8e0q.fsf@tassilo.jf.intel.com>
Date:	Wed, 25 Sep 2013 20:20:37 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Lin Ming <minggr@...il.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	Tejun Heo <tj@...nel.org>
Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"

Lin Ming <minggr@...il.com> writes:
>
> Would you like below patch?

The loop body keeps rather complex state. It could easily 
get confused by parallel RCU changes.

So if the list changes in parallel you may suddenly
report very bogus values, as the va_start - prev_end 
computation may be bogus.

Perhaps it's ok (may report bogus gaps), but it seems a bit risky.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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