Re: [PATCH v13 08/15] crash: Add crash_prepare_headers() to exclude crash kernel memory

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Calling `get_online_mems()` inside `crash_prepare_headers()` creates an AA self-deadlock when executed from the memory hotplug notifier path.
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commit 40b18d3ef2c2d34f758c8077fa6b20ad0d951107
Author: Jinjie Ruan <ruanjinjie@huawei.com>

crash: Add crash_prepare_headers() to exclude crash kernel memory

This commit introduces a common crash_prepare_headers() helper to consolidate
crash memory allocation and exclusion logic across architectures. It adds
three new architecture-specific functions to gather memory ranges and builds
the ELF core headers for the crash kernel.

> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 2c1a3791e4101..c50c25937d7d4 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c

[ ... ]

> +int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
> +			  unsigned long *nr_mem_ranges)
> +{
> +	unsigned int max_nr_ranges;
> +	struct crash_mem *cmem;
> +	int ret;
> +
> +	get_online_mems();

Could this cause an AA self-deadlock when crash_prepare_headers() is used
by arch_crash_handle_hotplug_event() to handle memory hotplug events?

When memory is hotplugged, online_pages() or offline_pages() trigger the
memory_notify() chain. online_pages() is invoked with the mem_hotplug_lock
already held for write via mem_hotplug_begin() (which maps to
percpu_down_write(&mem_hotplug_lock)).

If the hotplug notifier invokes the crash handler to update the ELF headers,
the current thread attempts to acquire the same lock for read here in
get_online_mems().

Since the Linux percpu_rw_semaphore does not support recursive read-lock
acquisition by the active writer, will the thread fail the trylock and sleep
indefinitely in percpu_rwsem_wait(), causing a deadlock?

> +	max_nr_ranges = arch_get_system_nr_ranges();
> +	if (!max_nr_ranges) {
> +		put_online_mems();
> +		return -ENOMEM;
> +	}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260511030454.1730881-1-ruanjinjie@huawei.com?part=8