Re: [Ocfs2-devel] [PATCH V2] ocfs2: fix dead lock caused by ocfs2_defrag_extent

[Larry Chen]

Hi Changwei,

Thanks for your review, I'll improve my patch and resend it later.

Thanks
Larry

On 11/1/18 11:11 AM, Changwei Ge wrote:
> Hi Larry,
>
> I still have a few tiny comments for your patch, please refer to them.
>
> On 2018/11/1 5:28, Andrew Morton wrote:
> > Folks, could we please review this patch for upstream inclusion?
> >
> > Thanks.
> >
> >
> > From: Larry Chen <lchen@xxxxxxxx>
> > Subject: ocfs2: fix deadlock caused by ocfs2_defrag_extent
> >
> > ocfs2_defrag_extent may fall into deadlock.
> >
> > ocfs2_ioctl_move_extents
> >     ocfs2_ioctl_move_extents
> >       ocfs2_move_extents
> >         ocfs2_defrag_extent
> >           ocfs2_lock_allocators_move_extents
> >
> >             ocfs2_reserve_clusters
> >               inode_lock GLOBAL_BITMAP_SYSTEM_INODE
> >
> > 	  __ocfs2_flush_truncate_log
> >               inode_lock GLOBAL_BITMAP_SYSTEM_INODE
> >
> > As backtrace shows above, ocfs2_reserve_clusters() will call inode_lock
> > against the global bitmap if local allocator has not sufficient cluters.
> > Once global bitmap could meet the demand, ocfs2_reserve_cluster will
> > return success with global bitmap locked.
> >
> > After ocfs2_reserve_cluster(), if truncate log is full,
> > __ocfs2_flush_truncate_log() will definitely fall into deadlock because it
> > needs to inode_lock global bitmap, which has already been locked.
> >
> > To fix this bug, we could remove from ocfs2_lock_allocators_move_extents()
> > the code which intends to lock global allocator, and put the removed code
> > after __ocfs2_flush_truncate_log().
> >
> > ocfs2_lock_allocators_move_extents() is refered by 2 places, one is here,
> > the other does not need the data allocator context, which means this patch
> > does not affect the caller so far.
> >
> > [lchen@xxxxxxxx: rename ocfs2_lock_allocators_move_extents() to ocfs2_lock_meta_allocator_move_extents(), add some comments]
> >     Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_20180902091455.23862-2D1-2Dlchen-40suse.com&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=C7gAd4uDxlAvTdc0vmU6X8CMk6L2iDY8-HD0qT6Fo7Y&m=K8aRgOiMescamJW-IuHq-cW4mWedGQv2JTT-2KPy1RI&s=3fQHFtwgixirPeQ5Px4fRBnd_UcSx3rvSsLKLidwESo&e=
> > Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_20180827080121.31145-2D1-2Dlchen-40suse.com&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=C7gAd4uDxlAvTdc0vmU6X8CMk6L2iDY8-HD0qT6Fo7Y&m=K8aRgOiMescamJW-IuHq-cW4mWedGQv2JTT-2KPy1RI&s=PQOJREyeElsg_1IlINdSGefNqA6w_cUrI1ezdVxyi7o&e=
> > Signed-off-by: Larry Chen <lchen@xxxxxxxx>
> > Cc: Mark Fasheh <mark@xxxxxxxxxx>
> > Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
> > Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> > Cc: Joseph Qi <jiangqi903@xxxxxxxxx>
> > Cc: Changwei Ge <ge.changwei@xxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >
> >    fs/ocfs2/move_extents.c |   40 +++++++++++++++++++++++---------------
> >    1 file changed, 25 insertions(+), 15 deletions(-)
> >
> > --- a/fs/ocfs2/move_extents.c~fix-dead-lock-caused-by-ocfs2_defrag_extent
> > +++ a/fs/ocfs2/move_extents.c
> > @@ -162,7 +162,7 @@ out:
> >     * in some cases, we don't need to reserve clusters, just let data_ac
> >     * be NULL.
> >     */
> > -static int ocfs2_lock_allocators_move_extents(struct inode *inode,
> > +static int ocfs2_lock_meta_allocator_move_extents(struct inode *inode,
> >    					struct ocfs2_extent_tree *et,
> >    					u32 clusters_to_move,
> >    					u32 extents_to_split,
>
> After removing 'reserving clusters logic' out of this function, I suggest to also change the function header comments.
> And I think there is no need for arguments _data_ac_ now.
> Otherwise this patch looks sane to me.
>
> Thanks,
> Changwei
>
> > @@ -192,13 +192,6 @@ static int ocfs2_lock_allocators_move_ex
> >    		goto out;
> >    	}
> >    
> > -	if (data_ac) {
> > -		ret = ocfs2_reserve_clusters(osb, clusters_to_move, data_ac);
> > -		if (ret) {
> > -			mlog_errno(ret);
> > -			goto out;
> > -		}
> > -	}
> >    
> >    	*credits += ocfs2_calc_extend_credits(osb->sb, et->et_root_el);
> >    
> > @@ -257,10 +250,11 @@ static int ocfs2_defrag_extent(struct oc
> >    		}
> >    	}
> >    
> > -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, *len, 1,
> > -						 &context->meta_ac,
> > -						 &context->data_ac,
> > -						 extra_blocks, &credits);
> > +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
> > +						*len, 1,
> > +						&context->meta_ac,
> > +						&context->data_ac,
> > +						extra_blocks, &credits);
> >    	if (ret) {
> >    		mlog_errno(ret);
> >    		goto out;
> > @@ -283,6 +277,21 @@ static int ocfs2_defrag_extent(struct oc
> >    		}
> >    	}
> >    
> > +	/*
> > +	 * Make sure ocfs2_reserve_cluster is called after
> > +	 * __ocfs2_flush_truncate_log, otherwise, dead lock may happen.
> > +	 *
> > +	 * If ocfs2_reserve_cluster is called
> > +	 * before __ocfs2_flush_truncate_log, dead lock on global bitmap
> > +	 * may happen.
> > +	 *
> > +	 */
> > +	ret = ocfs2_reserve_clusters(osb, *len, &context->data_ac);
> > +	if (ret) {
> > +		mlog_errno(ret);
> > +		goto out_unlock_mutex;
> > +	}
> > +
> >    	handle = ocfs2_start_trans(osb, credits);
> >    	if (IS_ERR(handle)) {
> >    		ret = PTR_ERR(handle);
> > @@ -600,9 +609,10 @@ static int ocfs2_move_extent(struct ocfs
> >    		}
> >    	}
> >    
> > -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, len, 1,
> > -						 &context->meta_ac,
> > -						 NULL, extra_blocks, &credits);
> > +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
> > +						len, 1,
> > +						&context->meta_ac,
> > +						NULL, extra_blocks, &credits);
> >    	if (ret) {
> >    		mlog_errno(ret);
> >    		goto out;
> > _
> >
> >
> > _______________________________________________
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