xfs: use __GFP_NOLOCKDEP instead of GFP_NOFS
In the past we've had problems with lockdep false positives stemming from inode locking occurring in memory reclaim contexts (e.g. from superblock shrinkers). Lockdep doesn't know that inodes access from above memory reclaim cannot be accessed from below memory reclaim (and vice versa) but there has never been a good solution to solving this problem with lockdep annotations. This situation isn't unique to inode locks - buffers are also locked above and below memory reclaim, and we have to maintain lock ordering for them - and against inodes - appropriately. IOWs, the same code paths and locks are taken both above and below memory reclaim and so we always need to make sure the lock orders are consistent. We are spared the lockdep problems this might cause by the fact that semaphores and bit locks aren't covered by lockdep. In general, this sort of lockdep false positive detection is cause by code that runs GFP_KERNEL memory allocation with an actively referenced inode locked. When it is run from a transaction, memory allocation is automatically GFP_NOFS, so we don't have reclaim recursion issues. So in the places where we do memory allocation with inodes locked outside of a transaction, we have explicitly set them to use GFP_NOFS allocations to prevent lockdep false positives from being reported if the allocation dips into direct memory reclaim. More recently, __GFP_NOLOCKDEP was added to the memory allocation flags to tell lockdep not to track that particular allocation for the purposes of reclaim recursion detection. This is a much better way of preventing false positives - it allows us to use GFP_KERNEL context outside of transactions, and allows direct memory reclaim to proceed normally without throwing out false positive deadlock warnings. The obvious places that lock inodes and do memory allocation are the lookup paths and inode extent list initialisation. These occur in non-transactional GFP_KERNEL contexts, and so can run direct reclaim and lock inodes. This patch makes a first path through all the explicit GFP_NOFS allocations in XFS and converts the obvious ones to GFP_KERNEL | __GFP_NOLOCKDEP as a first step towards removing explicit GFP_NOFS allocations from the XFS code. Signed-off-by:Dave Chinner <dchinner@redhat.com> Reviewed-by:
"Darrick J. Wong" <djwong@kernel.org> Signed-off-by:
Chandan Babu R <chandanbabu@kernel.org>
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