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Deepanshu Kartikey cec944dd32 hugetlbfs: move lock assertions after early returns in huge_pmd_unshare() 
When hugetlb_vmdelete_list() processes VMAs during truncate operations, it
may encounter VMAs where huge_pmd_unshare() is called without the required
shareable lock.  This triggers an assertion failure in
hugetlb_vma_assert_locked().

The previous fix in commit dd83609b88 ("hugetlbfs: skip VMAs without
shareable locks in hugetlb_vmdelete_list") skipped entire VMAs without
shareable locks to avoid the assertion.  However, this prevented pages
from being unmapped and freed, causing a regression in
fallocate(PUNCH_HOLE) operations where pages were not freed immediately,
as reported by Mark Brown.

Instead of checking locks in the caller or skipping VMAs, move the lock
assertions in huge_pmd_unshare() to after the early return checks.  The
assertions are only needed when actual PMD unsharing work will be
performed.  If the function returns early because sz != PMD_SIZE or the
PMD is not shared, no locks are required and assertions should not fire.

This approach reverts the VMA skipping logic from commit dd83609b88
("hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list")
while moving the assertions to avoid the assertion failure, keeping all
the logic within huge_pmd_unshare() itself and allowing page unmapping and
freeing to proceed for all VMAs.

Link: https://lkml.kernel.org/r/20251014113344.21194-1-kartikey406@gmail.com
Fixes: dd83609b88 ("hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reported-by: <syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com>
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://syzkaller.appspot.com/bug?extid=f26d7c75c26ec19790e7
Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Oscar Salvador <osalvador@suse.de>
Tested-by: <syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2025-10-21 15:46:17 -07:00
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README 

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.