tree feba3440f6d2c5008f8cc678a6f4a0d5359b79eb
parent fc19e231688cc244f38c46d8fdcff2ba80f43fbf
author Waiman Long <longman@redhat.com> 1719360999 -0400
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1721301670 +0200

mm: prevent derefencing NULL ptr in pfn_section_valid()

[ Upstream commit 82f0b6f041fad768c28b4ad05a683065412c226e ]

Commit 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing
memory_section->usage") changed pfn_section_valid() to add a READ_ONCE()
call around "ms->usage" to fix a race with section_deactivate() where
ms->usage can be cleared.  The READ_ONCE() call, by itself, is not enough
to prevent NULL pointer dereference.  We need to check its value before
dereferencing it.

Link: https://lkml.kernel.org/r/20240626001639.1350646-1-longman@redhat.com
Fixes: 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage")
Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>