Messages in this thread Patch in this message | | | Date | Fri, 21 Nov 2014 09:30:36 -0500 | From | Pranith Kumar <> | Subject | Re: [PATCH tip/core/rcu 3/9] drivers/md: Use rcu_dereference() for accessing rcu pointer |
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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 >
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