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

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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))



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