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A prior commite0f3c3f78d("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 commit35cfa2b0b4("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.