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We have seen bugs and resource leaks arise from the complexity of the __mmap_region() function. This, and the generally deeply fragile error handling logic and complexity which makes understanding the function difficult make it highly desirable to refactor it into something readable. Achieve this by separating the function into smaller logical parts which are easier to understand and follow, and which importantly very significantly simplify the error handling. Note that we now call vms_abort_munmap_vmas() in more error paths than we used to, however in cases where no abort need occur, vms->nr_pages will be equal to zero and we simply exit this function without doing more than we would have done previously. Importantly, the invocation of the driver mmap hook via mmap_file() now has very simple and obvious handling (this was previously the most problematic part of the mmap() operation). Use a generalised stack-based 'mmap state' to thread through values and also retrieve state as needed. Also avoid ever relying on vma merge (vmg) state after a merge is attempted, instead maintain meaningful state in the mmap state and establish vmg state as and when required. This avoids any subtle bugs arising from merge logic mutating this state and mmap_region() logic later relying upon it. Link: https://lkml.kernel.org/r/25bd2edc3275450f448cbfe0756ce2a7cd06810f.1729858176.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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 reStructuredText 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.