mm/mmu_notifiers: do not speculatively allocate a mmu_notifier_mm
A prior commit e0f3c3f7 ("mm/mmu_notifier: init notifier if necessary") made an attempt at doing this, but had to be reverted as calling the GFP_KERNEL allocator under the i_mmap_mutex causes deadlock, see commit 35cfa2b0 ("mm/mmu_notifier: allocate mmu_notifier in advance"). However, we can avoid that problem by doing the allocation only under the mmap_sem, which is already happening. Since all writers to mm->mmu_notifier_mm hold the write side of the mmap_sem reading it under that sem is deterministic and we can use that to decide if the allocation path is required, without speculation. The actual update to mmu_notifier_mm must still be done under the mm_take_all_locks() to ensure read-side coherency. Link: https://lore.kernel.org/r/20190806231548.25242-3-jgg@ziepe.ca Reviewed-by:Christoph Hellwig <hch@lst.de> Reviewed-by:
Ralph Campbell <rcampbell@nvidia.com> Tested-by:
Ralph Campbell <rcampbell@nvidia.com> Signed-off-by:
Jason Gunthorpe <jgg@mellanox.com>
parent
56c57103
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