Re: [PATCH v6 13/17] iommu/arm-smmu-v3: Add streams_lock for atomic-context SID->master lookup

[sashiko-bot@kernel.org]

> A subsequent change will look up arm_smmu_master entries by SID from inside
> arm_smmu_cmdq_batch_retry(), which runs with invs->rwlock read_lock held in
> IRQ-disabled context, and so cannot take the sleeping streams_mutex.
> 
> Add a spinlock_t streams_lock that protects rb_root mutations alongside the
> existing streams_mutex:
>  - atomic-context readers will hold the spinlock alone
>  - writers (insert/remove paths) take both
> 
> A reader under the streams_lock uses all the streams of the found master,
> so the insertion has to be all-or-nothing: make arm_smmu_insert_master()
> initialize all the L2 strtabs first and then insert all the stream nodes in
> one critical section, making a master found via any single SID always fully
> initialized.
> 
> Update the lockdep assertion in arm_smmu_find_master() to accept either of
> the locks so the helper is callable from both contexts.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Assisted-by: LLM
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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