From: Dave Chinner <dchinner@xxxxxxxxxx> We've had a few reports of lockdep tripping over memory reclaim context vs filesystem freeze "deadlocks". They all have looked to be false positives on analysis, but it seems that they are being tripped because we take freeze references before we run a GFP_KERNEL allocation for the struct xfs_trans. We can avoid this false positive vector just by re-ordering the operations in xfs_trans_alloc(). That is. we need allocate the structure before we take the freeze reference and enter the GFP_NOFS allocation context that follows the xfs_trans around. This prevents lockdep from seeing the GFP_KERNEL allocation inside the transaction context, and that prevents it from triggering the freeze level vs alloc context vs reclaim warnings. Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> --- fs/xfs/xfs_trans.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c index bedc5a5133a5..912b42f5fe4a 100644 --- a/fs/xfs/xfs_trans.c +++ b/fs/xfs/xfs_trans.c @@ -259,6 +259,14 @@ xfs_trans_alloc( struct xfs_trans *tp; int error; + /* + * Allocate the handle before we do our freeze accounting and setting up + * GFP_NOFS allocation context so that we avoid lockdep false positives + * by doing GFP_KERNEL allocations inside sb_start_intwrite(). + */ + tp = kmem_zone_zalloc(xfs_trans_zone, + (flags & XFS_TRANS_NOFS) ? KM_NOFS : KM_SLEEP); + if (!(flags & XFS_TRANS_NO_WRITECOUNT)) sb_start_intwrite(mp->m_super); @@ -270,8 +278,6 @@ xfs_trans_alloc( mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE); atomic_inc(&mp->m_active_trans); - tp = kmem_zone_zalloc(xfs_trans_zone, - (flags & XFS_TRANS_NOFS) ? KM_NOFS : KM_SLEEP); tp->t_magic = XFS_TRANS_HEADER_MAGIC; tp->t_flags = flags; tp->t_mountp = mp; -- 2.17.0
