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

[Kefeng Wang]

On 2023/4/18 11:13, HORIGUCHI NAOYA(堀口 直也) wrote:
> 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@xxxxxxxxxxxxxxxxxx>
> > Cc: Christian Brauner <brauner@xxxxxxxxxx>
> > Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> > Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> > Cc: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> > Cc: Jens Axboe <axboe@xxxxxxxxx>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> > 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?

For dump_user_range(), the task is dying, if copy incomplete size, the 
coredump will fail and task will exit, also memory_failure will
be called by kill_me_maybe(),

 CPU: 0 PID: 1418 Comm: test Tainted: G   M               6.3.0-rc5 #29
 Call Trace:
  <TASK>
  dump_stack_lvl+0x37/0x50
  memory_failure+0x51/0x970
  kill_me_maybe+0x5b/0xc0
  task_work_run+0x5a/0x90
  exit_to_user_mode_prepare+0x194/0x1a0
  irqentry_exit_to_user_mode+0x9/0x30
  noist_exc_machine_check+0x40/0x80
  asm_exc_machine_check+0x33/0x40


> 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))