Re: [PATCH v1 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas

[Baoquan He <bhe@redhat.com>]

On 12/04/22 at 11:47am, kernel test robot wrote:
> Hi Baoquan,
> 
> I love your patch! Perhaps something to improve:
> 
> [auto build test WARNING on akpm-mm/mm-everything]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221204-093322
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/20221204013046.154960-4-bhe%40redhat.com
> patch subject: [PATCH v1 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas
> config: arm-randconfig-r046-20221204
> compiler: arm-linux-gnueabi-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/0bcc4ce1e46418b86eb569175879081116649727
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221204-093322
>         git checkout 0bcc4ce1e46418b86eb569175879081116649727
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    mm/vmalloc.c: In function 'vb_vread':
> >> mm/vmalloc.c:3540:23: warning: variable 'offset' set but not used [-Wunused-but-set-variable]
>     3540 |         unsigned long offset;
>          |                       ^~~~~~

Thanks.

The local variable 'offset' is needed, the handling in vb_vread() need
be improved to cover the case in which reading is started from dirty or
free regions. I will add below change to v2.


diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 78cae59170d8..6612914459cf 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3526,7 +3522,6 @@ static void vb_vread(char *buf, char *addr, int count)
 	unsigned long offset;
 	unsigned int rs, re, n;
 
-	offset = ((unsigned long)addr & (VMAP_BLOCK_SIZE - 1)) >> PAGE_SHIFT;
 	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
 
 	spin_lock(&vb->lock);
@@ -3547,16 +3542,22 @@ static void vb_vread(char *buf, char *addr, int count)
 			addr++;
 			count--;
 		}
-		n = (re - rs + 1) << PAGE_SHIFT;
+		/*it could start reading from the middle of used region*/
+		offset = offset_in_page(addr);
+		n = (re - rs + 1) << PAGE_SHIFT - offset;
 		if (n > count)
 			n = count;
-		aligned_vread(buf, start, n);
+		aligned_vread(buf, start+offset, n);
 
 		buf += n;
 		addr += n;
 		count -= n;
 	}
 	spin_unlock(&vb->lock);
+
+	/* zero-fill the left dirty or free regions */
+	if (count)
+		memset(buf, 0, count);
 }
 
 /**