mm: memory-failure: enhance comments for return value of memory_failure()

The comments for the return value of memory_failure are not complete,
supplement the comments.

Link: https://lkml.kernel.org/r/20250312112852.82415-4-xueshuai@linux.alibaba.com
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ruidong Tian <tianruidong@linux.alibaba.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: axiqia

mm/memory-failure.c

@@ -2215,9 +2215,13 @@ static void kill_procs_now(struct page *p, unsigned long pfn, int flags,
  * Must run in process context (e.g. a work queue) with interrupts
  * enabled and no spinlocks held.
  *
- * Return: 0 for successfully handled the memory error,
- *         -EOPNOTSUPP for hwpoison_filter() filtered the error event,
- *         < 0(except -EOPNOTSUPP) on failure.
+ * Return:
+ *   0             - success,
+ *   -ENXIO        - memory not managed by the kernel
+ *   -EOPNOTSUPP   - hwpoison_filter() filtered the error event,
+ *   -EHWPOISON    - the page was already poisoned, potentially
+ *                   kill process,
+ *   other negative values - failure.
  */
 int memory_failure(unsigned long pfn, int flags)
 {