Re: [PATCH v2] mm: hwpoison: coredump: support recovery from dump_user_range()

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Mon, Apr 17, 2023 at 12:53:23PM +0800, Kefeng Wang wrote:
> The dump_user_range() is used to copy the user page to a coredump file,
> but if a hardware memory error occurred during copy, which called from
> __kernel_write_iter() in dump_user_range(), it crashes,
> 
>   CPU: 112 PID: 7014 Comm: mca-recover Not tainted 6.3.0-rc2 #425
>  
>   pc : __memcpy+0x110/0x260
>   lr : _copy_from_iter+0x3bc/0x4c8
>   ...
>   Call trace:
>    __memcpy+0x110/0x260
>    copy_page_from_iter+0xcc/0x130
>    pipe_write+0x164/0x6d8
>    __kernel_write_iter+0x9c/0x210
>    dump_user_range+0xc8/0x1d8
>    elf_core_dump+0x308/0x368
>    do_coredump+0x2e8/0xa40
>    get_signal+0x59c/0x788
>    do_signal+0x118/0x1f8
>    do_notify_resume+0xf0/0x280
>    el0_da+0x130/0x138
>    el0t_64_sync_handler+0x68/0xc0
>    el0t_64_sync+0x188/0x190
> 
> Generally, the '->write_iter' of file ops will use copy_page_from_iter()
> and copy_page_from_iter_atomic(), change memcpy() to copy_mc_to_kernel()
> in both of them to handle #MC during source read, which stop coredump
> processing and kill the task instead of kernel panic, but the source
> address may not always a user address, so introduce a new copy_mc flag in
> struct iov_iter{} to indicate that the iter could do a safe memory copy,
> also introduce the helpers to set/cleck the flag, for now, it's only
> used in coredump's dump_user_range(), but it could expand to any other
> scenarios to fix the similar issue.
> 
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Miaohe Lin <linmiaohe@huawei.com>
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Cc: Tong Tiangen <tongtiangen@huawei.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v2:
> - move the helper functions under pre-existing CONFIG_ARCH_HAS_COPY_MC
> - reposition the copy_mc in struct iov_iter for easy merge, suggested
>   by Andrew Morton
> - drop unnecessary clear flag helper
> - fix checkpatch warning
>  fs/coredump.c       |  1 +
>  include/linux/uio.h | 16 ++++++++++++++++
>  lib/iov_iter.c      | 17 +++++++++++++++--
>  3 files changed, 32 insertions(+), 2 deletions(-)
> 
...
> @@ -371,6 +372,14 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
>  EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
>  #endif /* CONFIG_ARCH_HAS_COPY_MC */
>  
> +static void *memcpy_from_iter(struct iov_iter *i, void *to, const void *from,
> +				 size_t size)
> +{
> +	if (iov_iter_is_copy_mc(i))
> +		return (void *)copy_mc_to_kernel(to, from, size);

Is it helpful to call memory_failure_queue() if copy_mc_to_kernel() fails
due to a memory error?

Thanks,
Naoya Horiguchi

> +	return memcpy(to, from, size);
> +}
> +
>  size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
>  {
>  	if (WARN_ON_ONCE(!i->data_source))