Re: [PATCH 1/3] mm: Add kvrealloc()

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jun 30, 2021 at 04:14:29PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> During log recovery of an XFS filesystem with 64kB directory
> buffers, rebuilding a buffer split across two log records results
> in a memory allocation warning from krealloc like this:
> 
> xfs filesystem being mounted at /mnt/scratch supports timestamps until 2038 (0x7fffffff)
> XFS (dm-0): Unmounting Filesystem
> XFS (dm-0): Mounting V5 Filesystem
> XFS (dm-0): Starting recovery (logdev: internal)
> ------------[ cut here ]------------
> WARNING: CPU: 5 PID: 3435170 at mm/page_alloc.c:3539 get_page_from_freelist+0xdee/0xe40
> .....
> RIP: 0010:get_page_from_freelist+0xdee/0xe40
> Call Trace:
>  ? complete+0x3f/0x50
>  __alloc_pages+0x16f/0x300
>  alloc_pages+0x87/0x110
>  kmalloc_order+0x2c/0x90
>  kmalloc_order_trace+0x1d/0x90
>  __kmalloc_track_caller+0x215/0x270
>  ? xlog_recover_add_to_cont_trans+0x63/0x1f0
>  krealloc+0x54/0xb0
>  xlog_recover_add_to_cont_trans+0x63/0x1f0
>  xlog_recovery_process_trans+0xc1/0xd0
>  xlog_recover_process_ophdr+0x86/0x130
>  xlog_recover_process_data+0x9f/0x160
>  xlog_recover_process+0xa2/0x120
>  xlog_do_recovery_pass+0x40b/0x7d0
>  ? __irq_work_queue_local+0x4f/0x60
>  ? irq_work_queue+0x3a/0x50
>  xlog_do_log_recovery+0x70/0x150
>  xlog_do_recover+0x38/0x1d0
>  xlog_recover+0xd8/0x170
>  xfs_log_mount+0x181/0x300
>  xfs_mountfs+0x4a1/0x9b0
>  xfs_fs_fill_super+0x3c0/0x7b0
>  get_tree_bdev+0x171/0x270
>  ? suffix_kstrtoint.constprop.0+0xf0/0xf0
>  xfs_fs_get_tree+0x15/0x20
>  vfs_get_tree+0x24/0xc0
>  path_mount+0x2f5/0xaf0
>  __x64_sys_mount+0x108/0x140
>  do_syscall_64+0x3a/0x70
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Essentially, we are taking a multi-order allocation from kmem_alloc()
> (which has an open coded no fail, no warn loop) and then
> reallocating it out to 64kB using krealloc(__GFP_NOFAIL) and that is
> then triggering the above warning.
> 
> This is a regression caused by converting this code from an open
> coded no fail/no warn reallocation loop to using __GFP_NOFAIL.
> 
> What we actually need here is kvrealloc(), so that if contiguous
> page allocation fails we fall back to vmalloc() and we don't
> get nasty warnings happening in XFS.
> 
> Fixes: 771915c4f688 ("xfs: remove kmem_realloc()")
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_log_recover.c |  2 +-
>  include/linux/mm.h       |  2 ++
>  mm/util.c                | 15 +++++++++++++++
>  3 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 1721fce2ec94..fee4fbadea0a 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -2062,7 +2062,7 @@ xlog_recover_add_to_cont_trans(
>  	old_ptr = item->ri_buf[item->ri_cnt-1].i_addr;
>  	old_len = item->ri_buf[item->ri_cnt-1].i_len;
>  
> -	ptr = krealloc(old_ptr, len + old_len, GFP_KERNEL | __GFP_NOFAIL);
> +	ptr = kvrealloc(old_ptr, old_len, len + old_len, GFP_KERNEL);

kvrealloc can return null, so this needs to check for that and -ENOMEM,
right?  It'll suck that log recovery fails, but such is life.

--D

>  	memcpy(&ptr[old_len], dp, len);
>  	item->ri_buf[item->ri_cnt-1].i_len += len;
>  	item->ri_buf[item->ri_cnt-1].i_addr = ptr;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8ae31622deef..aa720bc0a1d0 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -827,6 +827,8 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags)
>  	return kvmalloc_array(n, size, flags | __GFP_ZERO);
>  }
>  
> +extern void *kvrealloc(const void *p, size_t oldsize, size_t newsize,
> +		gfp_t flags);
>  extern void kvfree(const void *addr);
>  extern void kvfree_sensitive(const void *addr, size_t len);
>  
> diff --git a/mm/util.c b/mm/util.c
> index a8bf17f18a81..1104339ad2ca 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -635,6 +635,21 @@ void kvfree_sensitive(const void *addr, size_t len)
>  }
>  EXPORT_SYMBOL(kvfree_sensitive);
>  
> +void *kvrealloc(const void *p, size_t oldsize, size_t newsize, gfp_t flags)
> +{
> +	void *newp;
> +
> +	if (oldsize >= newsize)
> +		return (void *)p;
> +	newp = kvmalloc(newsize, flags);
> +	if (!newp)
> +		return NULL;
> +	memcpy(newp, p, oldsize);
> +	kvfree(p);
> +	return newp;
> +}
> +EXPORT_SYMBOL(kvrealloc);
> +
>  static inline void *__page_rmapping(struct page *page)
>  {
>  	unsigned long mapping;
> -- 
> 2.31.1
>