Hi Will/Robin,
On 6/28/17 4:46 AM, Will Deacon wrote:
> Hi Ray,
>
> Robin and I have been bashing our heads against the tlb_sync_pending flag
> this morning, and we reckon it could have something to do with your timeouts
> on MMU-500.
>
> On Tue, Jun 27, 2017 at 09:43:19AM -0700, Ray Jui wrote:
>>>> Also, in a few occasions, I observed the following message during the
>>>> test, when multiple cores are involved:
>>>>
>>>> arm-smmu 64000000.mmu: TLB sync timed out -- SMMU may be deadlocked
>
> The tlb_sync_pending logic was written under the assumption of a global
> page-table lock, so it assumes that it only has to care about syncing
> flushes from the current CPU/context. That's not true anymore, and the
> current code can accidentally skip syncs and (what I think is happening in
> your case) allow concurrent syncs, which will potentially lead to timeouts
> if a CPU is unlucky enough to keep missing the Ack.
>
> Please can you try the diff below and see if it fixes things for you?
> This applies on top of my for-joerg/arm-smmu/updates branch, but note
> that I've only shown it to the compiler. Not tested at all.
>
> Will
>
Thanks for looking into this. I'm a bit busy at work but will certainly
find time to test the diff below. I hopefully will get to it later this
week.
Thanks,
Ray
> --->8
>
> diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
> index 127558d83667..cd8d7aaec161 100644
> --- a/drivers/iommu/io-pgtable.c
> +++ b/drivers/iommu/io-pgtable.c
> @@ -59,6 +59,7 @@ struct io_pgtable_ops *alloc_io_pgtable_ops(enum
> io_pgtable_fmt fmt,
> iop->cookie = cookie;
> iop->cfg = *cfg;
>
> + atomic_set(&iop->tlb_sync_pending, 0);
> return &iop->ops;
> }
>
> diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
> index 524263a7ae6f..b64580c9d03d 100644
> --- a/drivers/iommu/io-pgtable.h
> +++ b/drivers/iommu/io-pgtable.h
> @@ -1,5 +1,7 @@
> #ifndef __IO_PGTABLE_H
> #define __IO_PGTABLE_H
> +
> +#include <linux/atomic.h>
> #include <linux/bitops.h>
>
> /*
> @@ -165,7 +167,7 @@ void free_io_pgtable_ops(struct io_pgtable_ops *ops);
> struct io_pgtable {
> enum io_pgtable_fmt fmt;
> void *cookie;
> - bool tlb_sync_pending;
> + atomic_t tlb_sync_pending;
> struct io_pgtable_cfg cfg;
> struct io_pgtable_ops ops;
> };
> @@ -175,22 +177,20 @@ struct io_pgtable {
> static inline void io_pgtable_tlb_flush_all(struct io_pgtable *iop)
> {
> iop->cfg.tlb->tlb_flush_all(iop->cookie);
> - iop->tlb_sync_pending = true;
> + atomic_set_release(&iop->tlb_sync_pending, 1);
> }
>
> static inline void io_pgtable_tlb_add_flush(struct io_pgtable *iop,
> unsigned long iova, size_t size, size_t granule, bool leaf)
> {
> iop->cfg.tlb->tlb_add_flush(iova, size, granule, leaf, iop->cookie);
> - iop->tlb_sync_pending = true;
> + atomic_set_release(&iop->tlb_sync_pending, 1);
> }
>
> static inline void io_pgtable_tlb_sync(struct io_pgtable *iop)
> {
> - if (iop->tlb_sync_pending) {
> + if (atomic_xchg_relaxed(&iop->tlb_sync_pending, 0))
> iop->cfg.tlb->tlb_sync(iop->cookie);
> - iop->tlb_sync_pending = false;
> - }
> }
>
> /**
>
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