[PATCH] powerpc/mm: Add cond_resched() while removing hpte mappings

[Michael Ellerman]

Vaibhav Jain <vaibhav at linux.ibm.com> writes:
> While removing large number of mappings from hash page tables for
> large memory systems as soft-lockup is reported because of the time
> spent inside htap_remove_mapping() like one below:
>
>  watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
>  <snip>
>  NIP plpar_hcall+0x38/0x58
>  LR  pSeries_lpar_hpte_invalidate+0x68/0xb0
>  Call Trace:
>   0x1fffffffffff000 (unreliable)
>   pSeries_lpar_hpte_removebolted+0x9c/0x230
>   hash__remove_section_mapping+0xec/0x1c0
>   remove_section_mapping+0x28/0x3c
>   arch_remove_memory+0xfc/0x150
>   devm_memremap_pages_release+0x180/0x2f0
>   devm_action_release+0x30/0x50
>   release_nodes+0x28c/0x300
>   device_release_driver_internal+0x16c/0x280
>   unbind_store+0x124/0x170
>   drv_attr_store+0x44/0x60
>   sysfs_kf_write+0x64/0x90
>   kernfs_fop_write+0x1b0/0x290
>   __vfs_write+0x3c/0x70
>   vfs_write+0xd4/0x270
>   ksys_write+0xdc/0x130
>   system_call+0x5c/0x70
>
> Fix this by adding a cond_resched() to the loop in
> htap_remove_mapping() that issues hcall to remove hpte mapping. This
> should prevent the soft-lockup from being reported.

Can/should we also/instead be using H_BLOCK_REMOVE?

cheers