linux-kernel - Re: [patch] mm: fix a race condition under SMC + COW

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Message-ID: <20060927172355.B12423@unix-os.sc.intel.com>
Date:	Wed, 27 Sep 2006 17:23:55 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	David Miller <davem@...emloft.net>
Cc:	suresh.b.siddha@...el.com, akpm@...l.org, hugh@...itas.com,
	linux-kernel@...r.kernel.org, asit.k.mallick@...el.com
Subject: Re: [patch] mm: fix a race condition under SMC + COW

On Wed, Sep 27, 2006 at 03:54:42PM -0700, David Miller wrote:
> You can't really do a set_pte_at() in this code path because
> there isn't a subsequent flush_tlb_*().
> 
> This is needed because some architectures queue up all set_pte_at()
> calls until the next flush_tlb_*() in order to batch TLB flushes.
> PowerPC and Sparc64 both do this.
> 
> The pte_establish() in the existing code works fine because it takes
> care of the set_pte_at() and flush_tlb_*() work internally when
> necessary on a given platform.

I am flushing the pte entry in ptep_clear_flush() and it is Ok not
to do another TLB flush after doing set_pte_at().

On Sparc64, this new set_pte_at() (after ptep_clear_flush) will not batch
any TLB flush as the previous pte contents were zero.

We are Ok with this patch, isn't it?

thanks,
suresh
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