Re: [PATCH V2] IB/hfi1,IB/qib: Fix qp_stats sleep with rcu read lock held

[Leon Romanovsky <leon@kernel.org>]

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On Fri, Aug 12, 2016 at 11:17:37AM -0400, ira.weiny@intel.com wrote:
> From: Mike Marciniszyn <mike.marciniszyn@intel.com>
> 
> The qp init function does a kzalloc() while holding the RCU
> lock that encounters the following warning with a debug kernel
> when a cat of the qp_stats is done:
> 
> [  231.723948] rcu_scheduler_active = 1, debug_locks = 0
> [  231.731939] 3 locks held by cat/11355:
> [  231.736492]  #0:  (debugfs_srcu){......}, at: [<ffffffff813001a5>] debugfs_use_file_start+0x5/0x90
> [  231.746955]  #1:  (&p->lock){+.+.+.}, at: [<ffffffff81289a6c>] seq_read+0x4c/0x3c0
> [  231.755873]  #2:  (rcu_read_lock){......}, at: [<ffffffffa0a0c535>] _qp_stats_seq_start+0x5/0xd0 [hfi1]
> [  231.766862]
> 
> The init functions do an implicit next which requires the rcu read lock
> before the kzalloc().
> 
> Fix for both drivers is to change the scope of the init function to only
> do the allocation and the initialization of the just allocated iter.
> 
> The implict next is moved back into the respective start functions to fix
> the issue.
> 
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
> CC: <stable@vger.kernel.org> # 4.6.x-
> 
> ---
> Changes from V1:
> 	use do.. while loop to execute first iter call.

Thanks,
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>

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