On Mon, May 18, 2020 at 07:07:21PM +0800, Anand Jain wrote: > > > On 16/5/20 11:43 am, Anand Jain wrote: > > On 16/5/20 1:40 am, David Sterba wrote: > >> On Thu, May 14, 2020 at 03:46:59AM +0800, Anand Jain wrote: > >>> A full list of tests just started. > >>> > >>> fs/btrfs/volumes.c | 8 +++++--- > >>> 1 file changed, 5 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > >>> index 60ab41c12e50..ebc8565d0f73 100644 > >>> --- a/fs/btrfs/volumes.c > >>> +++ b/fs/btrfs/volumes.c > >>> @@ -984,7 +984,6 @@ static struct btrfs_fs_devices > >>> *clone_fs_devices(struct btrfs_fs_devices *orig) > >>> if (IS_ERR(fs_devices)) > >>> return fs_devices; > >> > >> So now here's the device_list_mutex taken by a caller but inside > >> clone_fs_devices there's > >> > >> fs_devices = alloc_fs_devices(orig->fsid, NULL); > >> > >> just before this line and it does a GFP_KERNEL allocation. > > > > Oh right the allocations. Its not just about the other locks > > as I thought before. > > > > There are two ways to fix. > > Use GFP_NOFS > > I am not yet sure if it not possible. There were some previous > > work on the GFP flags. I need to review them. or, > > Move the allocation outside the locks. > > > > Looking into both of these choices. > > > > > Nack. On this patch. > > In general GFP_KERNEL is preferred over GFP_NOFS. For example. > > -------- > 6165572c btrfs: use GFP_KERNEL in btrfs_init_dev_replace_tgtdev > cc8385b5 btrfs: preallocate radix tree node for readahead > 78f2c9e6 btrfs: device add and remove: use GFP_KERNEL > -------- > > And there are quite a lot of GFP_KERNEL allocation along the > path leading to clone_fs_devices(). For that we have the scoped NOFS, using the memalloc_nofs_save/memalloc_nofs_restore. So if this is set before/after the device_list_mutex is taken when calling the cloning then it's safe with any potential GFP_KERNEL allocations on the way.
