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[ Upstream commit1e57ffb6e3] Think about the below scene: CPU1 CPU2 memunmap_pages percpu_ref_exit __percpu_ref_exit free_percpu(percpu_count); /* percpu_count is freed here! */ get_dev_pagemap xa_load(&pgmap_array, PHYS_PFN(phys)) /* pgmap still in the pgmap_array */ percpu_ref_tryget_live(&pgmap->ref) if __ref_is_percpu /* __PERCPU_REF_ATOMIC_DEAD not set yet */ this_cpu_inc(*percpu_count) /* access freed percpu_count here! */ ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD; /* too late... */ pageunmap_range To fix the issue, do percpu_ref_exit() after pgmap_array is emptied. So we won't do percpu_ref_tryget_live() against a being freed percpu_ref. Link: https://lkml.kernel.org/r/20220609121305.2508-1-linmiaohe@huawei.com Fixes:b7b3c01b19("mm/memremap_pages: support multiple ranges per invocation") Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Cc: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.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 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.