From: Minchan Kim <minchan.kim@gmail.com>
To: linux-mm <linux-mm@kvack.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Christoph Lameter <cl@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Question about pte_offset_map_lock
Date: Thu, 17 Dec 2009 11:46:30 +0900 [thread overview]
Message-ID: <20091217114630.d353907a.minchan.kim@barrios-desktop> (raw)
It may be a dumb question.
As I read the code of pte_lock, I have a question.
Now, there is pte_offset_map_lock following as.
#define pte_offset_map_lock(mm, pmd, address, ptlp) \
({ \
spinlock_t *__ptl = pte_lockptr(mm, pmd); \
pte_t *__pte = pte_offset_map(pmd, address); \
*(ptlp) = __ptl; \
spin_lock(__ptl); \
__pte; \
})
Why do we grab the lock after getting __pte?
Is it possible that __pte might be changed before we grab the spin_lock?
Some codes in mm checks original pte by pte_same.
There are not-checked cases in proc. As looking over the cases,
It seems no problem. But in future, new user of pte_offset_map_lock
could mistake with that?
--
Kind regards,
Minchan Kim
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next reply other threads:[~2009-12-17 2:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-17 2:46 Minchan Kim [this message]
2009-12-17 8:01 ` Peter Zijlstra
2009-12-17 14:49 ` Minchan Kim
2009-12-17 9:54 ` Hugh Dickins
2009-12-17 15:02 ` Minchan Kim
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