On 1/26/26 10:35 AM, Marco Elver wrote:
That being said, I don't think it's wrong to write e.g.:
spin_lock(&updater_lock);
__acquire_shared(ssp);
...
// writes happen through rcu_assign_pointer()
// reads can happen through srcu_dereference_check()
...
__release_shared(ssp);
spin_unlock(&updater_lock);
, given holding the updater lock implies reader access.
And given the analysis is opt-in (CONTEXT_ANALYSIS := y), I think
it's a manageable problem.
I'd like to make context-analysis mandatory for the entire kernel tree.
If you have a different idea how we can solve this, please let us know.
One final note, usage of srcu_dereference_check() is rare enough:
arch/x86/kvm/hyperv.c: irq_rt = srcu_dereference_check(kvm->irq_routing,
&kvm->irq_srcu,
arch/x86/kvm/x86.c:
kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu,
1));
arch/x86/kvm/x86.c:
kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
drivers/gpio/gpiolib.c: label = srcu_dereference_check(desc->label,
&desc->gdev->desc_srcu,
drivers/hv/mshv_irq.c: girq_tbl =
srcu_dereference_check(partition->pt_girq_tbl,
drivers/hwtracing/stm/core.c: link = srcu_dereference_check(src->link,
&stm_source_srcu, 1);
drivers/infiniband/hw/hfi1/user_sdma.c: pq = srcu_dereference_check(fd->pq,
&fd->pq_srcu,
fs/quota/dquot.c: struct dquot *dquot =
srcu_dereference_check(
fs/quota/dquot.c: struct dquot *dquot =
srcu_dereference_check(
fs/quota/dquot.c: put[cnt] =
srcu_dereference_check(dquots[cnt], &dquot_srcu,
fs/quota/dquot.c: transfer_from[cnt] =
srcu_dereference_check(dquots[cnt],
include/linux/kvm_host.h: return
srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu,
virt/kvm/irqchip.c: irq_rt = srcu_dereference_check(kvm->irq_routing,
&kvm->irq_srcu,
, that I think it's easy enough to annotate these places with the above
suggestions in case you're trying out global enablement.
Has it ever been considered to add support in the clang compiler for a
variant of __must_hold() that expresses that one of two capabilities
must be held by the caller? I think that would remove the need to
annotate SRCU update-side code with __acquire_shared(ssp) and
__release_shared(ssp).
Thanks,
Bart.
