lkml.org 
[lkml]   [2014]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH tip/core/rcu 3/9] drivers/md: Use rcu_dereference() for accessing rcu pointer
On 11/21/2014 08:31 AM, Kirill A. Shutemov wrote:
> On Tue, Oct 28, 2014 at 03:09:56PM -0700, Paul E. McKenney wrote:
>> From: Pranith Kumar <bobby.prani@gmail.com>
>>
>> Got Paul's email wrong the first time.
>>
>> The map field in 'struct mapped_device' is an rcu pointer. Use rcu_dereference()
>> while accessing it.
>>
>> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
>> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> On current -next I see this:
>
> [ 6.388264] ===============================
> [ 6.389571] [ INFO: suspicious RCU usage. ]
> [ 6.390869] 3.18.0-rc5-next-20141121-08303-g44cae4530372 #2 Not tainted
> [ 6.392185] -------------------------------
> [ 6.393479] /home/kas/git/public/linux/drivers/md/dm.c:2853 suspicious rcu_dereference_check() usage!
> [ 6.394801]
> other info that might help us debug this:
>

Hi Kirill,

We are dereferencing an RCU pointer with the suspend_lock held which is causing this warning.

Can you please check if the following patch helps? Thanks!

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index a0ece87..e584e66 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2830,7 +2830,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
*/
int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
{
- struct dm_table *map = NULL;
+ struct dm_table *map = rcu_dereference(md->map);
int r = 0;

retry:
@@ -2850,8 +2850,6 @@ retry:
goto retry;
}

- map = rcu_dereference(md->map);
-
r = __dm_suspend(md, map, suspend_flags, TASK_INTERRUPTIBLE);
if (r)
goto out_unlock;


> [ 6.398714]
> rcu_scheduler_active = 1, debug_locks = 0
> [ 6.401247] 1 lock held by cryptsetup/159:
> [ 6.402522] #0: (&md->suspend_lock/1){+.+...}, at: [<ffffffff8179dd1d>] dm_suspend+0x3d/0x140
> [ 6.403848]
> stack backtrace:
> [ 6.406448] CPU: 3 PID: 159 Comm: cryptsetup Not tainted 3.18.0-rc5-next-20141121-08303-g44cae4530372 #2
> [ 6.407726] Hardware name: LENOVO 3460CC6/3460CC6, BIOS G6ET93WW (2.53 ) 02/04/2013
> [ 6.408982] 0000000000000001 ffff8800d3ac7c38 ffffffff81b00bbd 0000000000000011
> [ 6.410249] ffff8800d301a560 ffff8800d3ac7c68 ffffffff81153be7 ffff8800d3928800
> [ 6.411548] ffff8800d3928970 ffff8800d3928aa0 0000000000000001 ffff8800d3ac7ca8
> [ 6.412780] Call Trace:
> [ 6.413980] [<ffffffff81b00bbd>] dump_stack+0x4c/0x6e
> [ 6.415178] [<ffffffff81153be7>] lockdep_rcu_suspicious+0xe7/0x120
> [ 6.416364] [<ffffffff8179de1d>] dm_suspend+0x13d/0x140
> [ 6.417535] [<ffffffff817a2d80>] ? table_load+0x340/0x340
> [ 6.418749] [<ffffffff817a2f2b>] dev_suspend+0x1ab/0x260
> [ 6.419901] [<ffffffff817a2d80>] ? table_load+0x340/0x340
> [ 6.421038] [<ffffffff817a3781>] ctl_ioctl+0x251/0x540
> [ 6.422164] [<ffffffff812b6415>] ? mntput_no_expire+0x5/0x360
> [ 6.423280] [<ffffffff817a3a83>] dm_ctl_ioctl+0x13/0x20
> [ 6.424389] [<ffffffff812a6f98>] do_vfs_ioctl+0x308/0x540
> [ 6.425515] [<ffffffff81175d2d>] ? rcu_read_lock_held+0x6d/0x70
> [ 6.426601] [<ffffffff812b324e>] ? __fget_light+0xbe/0xd0
> [ 6.427686] [<ffffffff812a7251>] SyS_ioctl+0x81/0xa0
> [ 6.428760] [<ffffffff81b0d6ad>] system_call_fastpath+0x16/0x1b
>



\
 
 \ /
  Last update: 2014-11-21 16:01    [W:0.159 / U:2.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site