linux-kernel - Re: VM ops on 37-rc1

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Date:	Thu, 4 Nov 2010 11:00:54 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	"Shi, Alex" <alex.shi@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"pzijlstr@...hat.com" <pzijlstr@...hat.com>
Subject: Re: VM ops on 37-rc1

This is discuss and fixed in another LKML thread, thanks.

---
commit ff8b16d7e15a8ba2a6086645614a483e048e3fbf
Author: Wu Fengguang <fengguang.wu@...el.com>
Date:   Thu Nov 4 01:56:49 2010 +0800
                                     
    vmstat: fix offset calculation on void*
                                           
    Fix regression introduced by commit 79da826aee6 ("writeback: report
    dirty thresholds in /proc/vmstat").                                
                                       
    The incorrect pointer arithmetic can result in problems like this:
                                                                      
      BUG: unable to handle kernel paging request at 07c06d16         
      IP: [<c050c336>] strnlen+0x6/0x20                      
      Call Trace:                      
       [<c050a249>] ? string+0x39/0xe0
       [<c042be6b>] ? __wake_up_common+0x4b/0x80
       [<c050afcc>] ? vsnprintf+0x1ec/0x380     
       [<c04b380e>] ? seq_printf+0x2e/0x60 
       [<c04829a6>] ? vmstat_show+0x26/0x30
       [<c04b3bb6>] ? seq_read+0xa6/0x380  
       [<c04b3b10>] ? seq_read+0x0/0x380 
       [<c04d5d2f>] ? proc_reg_read+0x5f/0x90
       [<c049c4a1>] ? vfs_read+0xa1/0x140    
       [<c04d5cd0>] ? proc_reg_read+0x0/0x90
       [<c049c981>] ? sys_read+0x41/0x70    
       [<c0402bd0>] ? sysenter_do_call+0x12/0x26
                                                
    Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
    Cc: Michael Rubin <mrubin@...gle.com>                         
    Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
    Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

diff --git a/mm/vmstat.c b/mm/vmstat.c
index cd2e42b..42eac4d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -949,7 +949,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
        v[PGPGIN] /= 2;         /* sectors -> kbytes */
        v[PGPGOUT] /= 2;
 #endif
-       return m->private + *pos;
+       return (unsigned long *)m->private + *pos;
 }
 
 static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
--
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