From: "joerg.roedel-5C7GfCeVMHo@public.gmane.org" <joerg.roedel-5C7GfCeVMHo@public.gmane.org>
To: Hiroshi Doyu <hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Cc: "ohad-Ix1uc/W3ht7QT0dZR+AlfA@public.gmane.org"
<ohad-Ix1uc/W3ht7QT0dZR+AlfA@public.gmane.org>,
"chrisw-69jw2NvuJkxg9hUCZPvPmw@public.gmane.org"
<chrisw-69jw2NvuJkxg9hUCZPvPmw@public.gmane.org>,
"iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org"
<iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
"linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [v3.6 3/3] iommu/tegra: smmu: Fix unsleepable memory allocation at alloc_pdir()
Date: Tue, 17 Jul 2012 15:23:00 +0200 [thread overview]
Message-ID: <20120717132300.GK4213@amd.com> (raw)
In-Reply-To: <20120717.152524.175499431618552821.hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
On Tue, Jul 17, 2012 at 02:25:24PM +0200, Hiroshi Doyu wrote:
> The above spin_lock is always necessary. "as->lock" should be held to
> protect "as->pdir_page". Only when "as->pdir_page" is NULL,
> "as->pdir_page" would be allocated in "alloc_pdir()". Without this
> lock, the following race could happen:
>
>
> Without as->lock:
> A: B:
> i == 3
> pdir_page == NULL
> i == 3
> pdir_page == NULL
> pdir_page = a;
> pdir_page = b; !!!!!! OVERWRITTEN !!!!!!
>
Unless I am missing something, this is not the correct situation with my
patch. It would look more like this:
A: B:
i == 3
pdir_page == NULL
i == 3
pdir_page == NULL
take as->lock
/* race check */
pdir_page == NULL -> proceed /* spinning on as->lock */
pdir_page = a;
release as->lock
take as->lock
/* race check */
pdir_page != NULL -> return
This should be fine, no? Do I miss something?
Joerg
WARNING: multiple messages have this Message-ID (diff)
From: joerg.roedel@amd.com (joerg.roedel at amd.com)
To: linux-arm-kernel@lists.infradead.org
Subject: [v3.6 3/3] iommu/tegra: smmu: Fix unsleepable memory allocation at alloc_pdir()
Date: Tue, 17 Jul 2012 15:23:00 +0200 [thread overview]
Message-ID: <20120717132300.GK4213@amd.com> (raw)
In-Reply-To: <20120717.152524.175499431618552821.hdoyu@nvidia.com>
On Tue, Jul 17, 2012 at 02:25:24PM +0200, Hiroshi Doyu wrote:
> The above spin_lock is always necessary. "as->lock" should be held to
> protect "as->pdir_page". Only when "as->pdir_page" is NULL,
> "as->pdir_page" would be allocated in "alloc_pdir()". Without this
> lock, the following race could happen:
>
>
> Without as->lock:
> A: B:
> i == 3
> pdir_page == NULL
> i == 3
> pdir_page == NULL
> pdir_page = a;
> pdir_page = b; !!!!!! OVERWRITTEN !!!!!!
>
Unless I am missing something, this is not the correct situation with my
patch. It would look more like this:
A: B:
i == 3
pdir_page == NULL
i == 3
pdir_page == NULL
take as->lock
/* race check */
pdir_page == NULL -> proceed /* spinning on as->lock */
pdir_page = a;
release as->lock
take as->lock
/* race check */
pdir_page != NULL -> return
This should be fine, no? Do I miss something?
Joerg
next prev parent reply other threads:[~2012-07-17 13:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-02 11:26 [v3.6 1/3] Revert "iommu/tegra: smmu: Fix unsleepable memory allocation" Hiroshi DOYU
[not found] ` <1341228398-6878-1-git-send-email-hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2012-07-02 11:26 ` [v3.6 2/3] iommu/tegra: smmu: Remove unnecessary sanity check at alloc_pdir() Hiroshi DOYU
2012-07-02 11:26 ` [v3.6 3/3] iommu/tegra: smmu: Fix unsleepable memory allocation " Hiroshi DOYU
[not found] ` <1341228398-6878-3-git-send-email-hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2012-07-17 10:09 ` Joerg Roedel
2012-07-17 10:09 ` Joerg Roedel
[not found] ` <20120717100901.GH4213-5C7GfCeVMHo@public.gmane.org>
2012-07-17 12:25 ` Hiroshi Doyu
2012-07-17 12:25 ` Hiroshi Doyu
[not found] ` <20120717.152524.175499431618552821.hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2012-07-17 13:23 ` joerg.roedel-5C7GfCeVMHo [this message]
2012-07-17 13:23 ` joerg.roedel at amd.com
2012-07-18 8:50 ` Hiroshi Doyu
2012-07-18 8:50 ` Hiroshi Doyu
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