Stephen Warren <[email protected]> wrote @ Thu, 28 Jun 2012 18:57:18 +0200:
> On 06/28/2012 04:51 AM, Hiroshi DOYU wrote:
> > alloc_pdir() is called from smmu_iommu_domain_init() with spin_lock
> > held. memory allocations in alloc_pdir() had to be
> > atomic/unsleepable. Instead of converting into atomic allocation, this
> > patch once releases a lock, do the allocation, hold the lock again and
> > then see if it's raced or not in order to avoid introducing mutex.
>
> > ---
>
> You'd typically want to include a brief description of what changed from
> v1->v2 here, as a hint to reviewers re: what to concentrate on.
Ok, I'll.
> > +static int alloc_pdir(struct smmu_as *as, unsigned long *flags)
>
> > + spin_unlock_irqrestore(&as->lock, *flags);
> > + cnt = devm_kzalloc(smmu->dev,
> > + sizeof(cnt[0]) * SMMU_PDIR_COUNT, GFP_KERNEL);
> > + page = alloc_page(GFP_KERNEL | __GFP_DMA);
> > + spin_lock_irqsave(&as->lock, *flags);
> > +
> > + if (as->pdir_page) {
> > + /* We raced, free the redundant */
> > + err = -ENODEV;
> > + goto err_out;
> > }
>
> Is that really an error; it just means that something else allocated the
> same pdir already. Since the top of the function does:
>
> if (as->pdir_page)
> return 0;
>
> I'd expect to s/err = -ENODEV/err = 0/ inside that if condition that I
> quoted above, but still of cause "goto err_out" to free the now unneeded
> allocations.
>
> Aside from that, I think this looks reasonable.
I think that, in the case of race condition, the one which comes
later, should retry with the another ASID, which is incremented as
below. So I modified that the latter one returns with -EAGAIN, and try
with another ASID.
The complete patch follows this mail.
Changes:
Modified drivers/iommu/tegra-smmu.c
diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index ec656ec..f2c18fa 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -562,7 +562,7 @@ static int alloc_pdir(struct smmu_as *as, unsigned long
*flags)
if (as->pdir_page) {
/* We raced, free the redundant */
- err = -ENODEV;
+ err = -EAGAIN;
goto err_out;
}
@@ -799,8 +799,15 @@ static int smmu_iommu_domain_init(struct iommu_domain
*domain)
spin_lock_irqsave(&tmp->lock, flags);
if (!tmp->pdir_page) {
- as = tmp;
- goto found;
+ int err;
+
+ err = alloc_pdir(tmp, &flags);
+ if (!err) {
+ as = tmp;
+ goto found;
+ }
+ if (err == -EAGAIN)
+ continue;
}
spin_unlock_irqrestore(&tmp->lock, flags);
}
@@ -808,9 +815,6 @@ static int smmu_iommu_domain_init(struct iommu_domain
*domain)
return -ENODEV;
found:
- if (alloc_pdir(as, &flags) < 0)
- goto err_alloc_pdir;
-
spin_lock(&smmu->lock);
/* Update PDIR register */
@@ -826,10 +830,6 @@ found:
dev_dbg(smmu->dev, "smmu_as@%p\n", as);
return 0;
-
-err_alloc_pdir:
- spin_unlock_irqrestore(&as->lock, flags);
- return -ENODEV;
}
static void smmu_iommu_domain_destroy(struct iommu_domain *domain)
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