[PATCH v2 0/6] mm/devm_memremap_pages: Fix page release race

[Dan Williams <dan.j.williams@intel.com>]

Changes since v1 [1]:
- Fix a NULL-pointer deref crash in pci_p2pdma_release() (Logan)

- Refresh the p2pdma patch headers to match the format of other p2pdma
  patches (Bjorn)

- Collect Ira's reviewed-by

[1]: https://lore.kernel.org/lkml/155387324370.2443841.574715745262628837.stgit@dwillia2-desk3.amr.corp.intel.com/

---

Logan audited the devm_memremap_pages() shutdown path and noticed that
it was possible to proceed to arch_remove_memory() before all
potential page references have been reaped.

Introduce a new ->cleanup() callback to do the work of waiting for any
straggling page references and then perform the percpu_ref_exit() in
devm_memremap_pages_release() context.

For p2pdma this involves some deeper reworks to reference count
resources on a per-instance basis rather than a per pci-device basis. A
modified genalloc api is introduced to convey a driver-private pointer
through gen_pool_{alloc,free}() interfaces. Also, a
devm_memunmap_pages() api is introduced since p2pdma does not
auto-release resources on a setup failure.

The dax and pmem changes pass the nvdimm unit tests, and the p2pdma
changes should now pass testing with the pci_p2pdma_release() fix.
Jérôme, how does this look for HMM?

In general, I think these patches / fixes are suitable for v5.2-rc1 or
v5.2-rc2, and since they touch kernel/memremap.c, and other various
pieces of the core, they should go through the -mm tree. These patches
merge cleanly with the current state of -next, pass the nvdimm unit
tests, and are exposed to the 0day robot with no issues reported
(https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=libnvdimm-pending).

---

Dan Williams (6):
      drivers/base/devres: Introduce devm_release_action()
      mm/devm_memremap_pages: Introduce devm_memunmap_pages
      PCI/P2PDMA: Fix the gen_pool_add_virt() failure path
      lib/genalloc: Introduce chunk owners
      PCI/P2PDMA: Track pgmap references per resource, not globally
      mm/devm_memremap_pages: Fix final page put race


 drivers/base/devres.c             |   24 +++++++-
 drivers/dax/device.c              |   13 +---
 drivers/nvdimm/pmem.c             |   17 ++++-
 drivers/pci/p2pdma.c              |  115 +++++++++++++++++++++++--------------
 include/linux/device.h            |    1 
 include/linux/genalloc.h          |   55 ++++++++++++++++--
 include/linux/memremap.h          |    8 +++
 kernel/memremap.c                 |   23 ++++++-
 lib/genalloc.c                    |   51 ++++++++--------
 mm/hmm.c                          |   14 +----
 tools/testing/nvdimm/test/iomap.c |    2 +
 11 files changed, 217 insertions(+), 106 deletions(-)
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