Re: [PATCH 4/4] mm/memory-failure: Fall back to vma_address() when ->notify_failure() fails

[Miaohe Lin <linmiaohe@huawei.com>]

On 2022/8/27 1:18, Dan Williams wrote:
> In the case where a filesystem is polled to take over the memory failure
> and receives -EOPNOTSUPP it indicates that page->index and page->mapping
> are valid for reverse mapping the failure address. Introduce
> FSDAX_INVALID_PGOFF to distinguish when add_to_kill() is being called
> from mf_dax_kill_procs() by a filesytem vs the typical memory_failure()
> path.

Thanks for fixing.
I'm sorry but I can't find the bug report email. Do you mean mf_dax_kill_procs() can
pass an invalid pgoff to the add_to_kill()? But it seems pgoff is guarded against invalid
value by vma_interval_tree_foreach() in collect_procs_fsdax(). So pgoff should be an valid
value. Or am I miss something?

Thanks,
Miaohe Lin

> 
> Otherwise, vma_pgoff_address() is called with an invalid fsdax_pgoff
> which then trips this failing signature:
> 
>  kernel BUG at mm/memory-failure.c:319!
>  invalid opcode: 0000 [#1] PREEMPT SMP PTI
>  CPU: 13 PID: 1262 Comm: dax-pmd Tainted: G           OE    N 6.0.0-rc2+ #62
>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
>  RIP: 0010:add_to_kill.cold+0x19d/0x209
>  [..]
>  Call Trace:
>   <TASK>
>   collect_procs.part.0+0x2c4/0x460
>   memory_failure+0x71b/0xba0
>   ? _printk+0x58/0x73
>   do_madvise.part.0.cold+0xaf/0xc5
> 
> Fixes: c36e20249571 ("mm: introduce mf_dax_kill_procs() for fsdax case")
> Cc: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Darrick J. Wong <djwong@kernel.org>
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>
> Cc: Jane Chu <jane.chu@oracle.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Miaohe Lin <linmiaohe@huawei.com>
> Cc: Ritesh Harjani <riteshh@linux.ibm.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  mm/memory-failure.c |   22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 8a4294afbfa0..e424a9dac749 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -345,13 +345,17 @@ static unsigned long dev_pagemap_mapping_shift(struct vm_area_struct *vma,
>   * not much we can do.	We just print a message and ignore otherwise.
>   */
>  
> +#define FSDAX_INVALID_PGOFF ULONG_MAX
> +
>  /*
>   * Schedule a process for later kill.
>   * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
>   *
> - * Notice: @fsdax_pgoff is used only when @p is a fsdax page.
> - *   In other cases, such as anonymous and file-backend page, the address to be
> - *   killed can be caculated by @p itself.
> + * Note: @fsdax_pgoff is used only when @p is a fsdax page and a
> + * filesystem with a memory failure handler has claimed the
> + * memory_failure event. In all other cases, page->index and
> + * page->mapping are sufficient for mapping the page back to its
> + * corresponding user virtual address.
>   */
>  static void add_to_kill(struct task_struct *tsk, struct page *p,
>  			pgoff_t fsdax_pgoff, struct vm_area_struct *vma,
> @@ -367,11 +371,7 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
>  
>  	tk->addr = page_address_in_vma(p, vma);
>  	if (is_zone_device_page(p)) {
> -		/*
> -		 * Since page->mapping is not used for fsdax, we need
> -		 * calculate the address based on the vma.
> -		 */
> -		if (p->pgmap->type == MEMORY_DEVICE_FS_DAX)
> +		if (fsdax_pgoff != FSDAX_INVALID_PGOFF)
>  			tk->addr = vma_pgoff_address(fsdax_pgoff, 1, vma);
>  		tk->size_shift = dev_pagemap_mapping_shift(vma, tk->addr);
>  	} else
> @@ -523,7 +523,8 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
>  			if (!page_mapped_in_vma(page, vma))
>  				continue;
>  			if (vma->vm_mm == t->mm)
> -				add_to_kill(t, page, 0, vma, to_kill);
> +				add_to_kill(t, page, FSDAX_INVALID_PGOFF, vma,
> +					    to_kill);
>  		}
>  	}
>  	read_unlock(&tasklist_lock);
> @@ -559,7 +560,8 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
>  			 * to be informed of all such data corruptions.
>  			 */
>  			if (vma->vm_mm == t->mm)
> -				add_to_kill(t, page, 0, vma, to_kill);
> +				add_to_kill(t, page, FSDAX_INVALID_PGOFF, vma,
> +					    to_kill);
>  		}
>  	}
>  	read_unlock(&tasklist_lock);
> 
> 
> .
>