During an SSR(Sub-System Restart) process, the remoteproc driver will
try to read the crash reason from SMEM. The qcom_smem_get() backing such
operations does however take the hwspinlock (tcsr mutex), which might be
held by the dying remoteproc.
The associated timeout on the hwspin_lock_timeout_irqsave() would take
care of the system not hanging forever, but the get operation will fail,
unnecessarily delaying the process for the 'HWSPINLOCK_TIMEOUT' duration
(currently is '1s'), and finally resulting in failure to get crash
information from SMEM.
This timeout can be avoided by removing the hwspinlock in the
qcom_smem_get routine. SMEM ensures that the allocated item will only be
visible after the new item is safe to use by following a specific order
of updates.
In the private partition case, qcom_smem_get_private() will use
'offset_free_uncached' as a loop boundary when looking for existing
allocated items. The corresponding allocation will only update
offset_free_uncached once the item is fully initialized.
hdr->canary = SMEM_PRIVATE_CANARY;
hdr->item = cpu_to_le16(item);
hdr->size = cpu_to_le32(ALIGN(size, 8));
hdr->padding_data = cpu_to_le16(le32_to_cpu(hdr->size) - size);
hdr->padding_hdr = 0;
wmb();
le32_add_cpu(&phdr->offset_free_uncached, alloc_size);
The global partition is similar but uses the "entry->allocated" variable
to ensure the item is not visible to qcom_smem_get_global().
Signed-off-by: Tao Zhang <[email protected]>
---
drivers/soc/qcom/smem.c | 11 -----------
1 file changed, 11 deletions(-)
diff --git a/drivers/soc/qcom/smem.c b/drivers/soc/qcom/smem.c
index 690afc9a12f4..7191fa0c087f 100644
--- a/drivers/soc/qcom/smem.c
+++ b/drivers/soc/qcom/smem.c
@@ -655,8 +655,6 @@ static void *qcom_smem_get_private(struct qcom_smem *smem,
void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
{
struct smem_partition *part;
- unsigned long flags;
- int ret;
void *ptr = ERR_PTR(-EPROBE_DEFER);
if (!__smem)
@@ -665,12 +663,6 @@ void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
if (WARN_ON(item >= __smem->item_count))
return ERR_PTR(-EINVAL);
- ret = hwspin_lock_timeout_irqsave(__smem->hwlock,
- HWSPINLOCK_TIMEOUT,
- &flags);
- if (ret)
- return ERR_PTR(ret);
-
if (host < SMEM_HOST_COUNT && __smem->partitions[host].virt_base) {
part = &__smem->partitions[host];
ptr = qcom_smem_get_private(__smem, part, item, size);
@@ -681,10 +673,7 @@ void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
ptr = qcom_smem_get_global(__smem, item, size);
}
- hwspin_unlock_irqrestore(__smem->hwlock, &flags);
-
return ptr;
-
}
EXPORT_SYMBOL_GPL(qcom_smem_get);
base-commit: 39676dfe52331dba909c617f213fdb21015c8d10
--
2.25.1
On 1/1/2024 6:25 PM, Tao Zhang wrote:
> During an SSR(Sub-System Restart) process, the remoteproc driver will
> try to read the crash reason from SMEM. The qcom_smem_get() backing such
> operations does however take the hwspinlock (tcsr mutex), which might be
> held by the dying remoteproc.
>
> The associated timeout on the hwspin_lock_timeout_irqsave() would take
> care of the system not hanging forever, but the get operation will fail,
> unnecessarily delaying the process for the 'HWSPINLOCK_TIMEOUT' duration
> (currently is '1s'), and finally resulting in failure to get crash
> information from SMEM.
>
> This timeout can be avoided by removing the hwspinlock in the
> qcom_smem_get routine. SMEM ensures that the allocated item will only be
> visible after the new item is safe to use by following a specific order
> of updates.
>
> In the private partition case, qcom_smem_get_private() will use
> 'offset_free_uncached' as a loop boundary when looking for existing
> allocated items. The corresponding allocation will only update
> offset_free_uncached once the item is fully initialized.
>
> hdr->canary = SMEM_PRIVATE_CANARY;
> hdr->item = cpu_to_le16(item);
> hdr->size = cpu_to_le32(ALIGN(size, 8));
> hdr->padding_data = cpu_to_le16(le32_to_cpu(hdr->size) - size);
> hdr->padding_hdr = 0;
>
> wmb();
> le32_add_cpu(&phdr->offset_free_uncached, alloc_size);
>
> The global partition is similar but uses the "entry->allocated" variable
> to ensure the item is not visible to qcom_smem_get_global().
>
> Signed-off-by: Tao Zhang <[email protected]>
> ---
Reviewed-by: Chris Lew <[email protected]>
On Tue, 02 Jan 2024 07:55:12 +0530, Tao Zhang wrote:
> During an SSR(Sub-System Restart) process, the remoteproc driver will
> try to read the crash reason from SMEM. The qcom_smem_get() backing such
> operations does however take the hwspinlock (tcsr mutex), which might be
> held by the dying remoteproc.
>
> The associated timeout on the hwspin_lock_timeout_irqsave() would take
> care of the system not hanging forever, but the get operation will fail,
> unnecessarily delaying the process for the 'HWSPINLOCK_TIMEOUT' duration
> (currently is '1s'), and finally resulting in failure to get crash
> information from SMEM.
>
> [...]
Applied, thanks!
[1/1] qcom: smem: remove hwspinlock from item get routine
commit: 27825593c972abac86b9a4453a8c8c9a2c1ec60f
Best regards,
--
Bjorn Andersson <[email protected]>