On Tue, May 22, 2018 at 9:42 AM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > Hey Dan, > > On 21/05/18 06:07 PM, Dan Williams wrote: >> Without this change we could fail to register the teardown of >> devm_memremap_pages(). The likelihood of hitting this failure is tiny >> as small memory allocations almost always succeed. However, the impact >> of the failure is large given any future reconfiguration, or >> disable/enable, of an nvdimm namespace will fail forever as subsequent >> calls to devm_memremap_pages() will fail to setup the pgmap_radix >> since there will be stale entries for the physical address range. > > Sorry, I don't follow this. The change only seems to prevent a warning > from occurring in this situation. Won't pgmap_radix_release() still be > called regardless of whether this patch is applied? devm_add_action() does not call the release function, devm_add_action_or_reset() does. > But it looks to me like this patch doesn't quite solve the issue -- at > least when looking at dax/pmem.c: If devm_add_action_or_reset() fails, > then dax_pmem_percpu_kill() won't be registered as an action and the > percpu_ref will never get killed. Thus, dax_pmem_percpu_release() would > not get called and dax_pmem_percpu_exit() will hang waiting for a > completion that will never occur. So we probably need to add a kill call > somewhere on the failing path... Ah, true, good catch! We should manually kill in the !registered case. I think this means we need to pass in the custom kill routine, because for the pmem driver it's blk_freeze_queue_start().
