Public bug reported:
Description:
> 1) Some p2pdma user calls pci_alloc_p2pmem() to get some memory to DMA
> to taking a reference to the pgmap.
> 2) Another process unbinds the underlying p2pdma driver and the devm
> chain starts to unwind.
> 3) devm_memremap_pages_release() is called and it kills the reference
> and drop's it's last reference.
Oh! Yes, nice find. We need to wait for the percpu-ref to be dead and
all outstanding references dropped before we can proceed to
arch_remove_memory(), and I think this problem has been there since
day one because the final exit was always after devm_memremap_pages()
release which means arch_remove_memory() was always racing any final
put_page(). I'll take a look, it seems the arch_remove_pages() call
needs to be moved out-of-line to its own context and wait for the
final exit of the percpu-ref.
Target Release: 19.10
Target Kernel: 5.3
** Affects: intel
Importance: Undecided
Status: New
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: intel-kernel-19.10
** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1835349
Title:
Fix devm_memremap_pages shutdown handling
Status in intel:
New
Status in linux package in Ubuntu:
New
Bug description:
Description:
> 1) Some p2pdma user calls pci_alloc_p2pmem() to get some memory to DMA
> to taking a reference to the pgmap.
> 2) Another process unbinds the underlying p2pdma driver and the devm
> chain starts to unwind.
> 3) devm_memremap_pages_release() is called and it kills the reference
> and drop's it's last reference.
Oh! Yes, nice find. We need to wait for the percpu-ref to be dead and
all outstanding references dropped before we can proceed to
arch_remove_memory(), and I think this problem has been there since
day one because the final exit was always after devm_memremap_pages()
release which means arch_remove_memory() was always racing any final
put_page(). I'll take a look, it seems the arch_remove_pages() call
needs to be moved out-of-line to its own context and wait for the
final exit of the percpu-ref.
Target Release: 19.10
Target Kernel: 5.3
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