On Thu, Jul 19, 2018 at 05:44:53PM +0200, David Sterba wrote:
> On Thu, Jul 19, 2018 at 06:35:33PM +0300, Nikolay Borisov wrote:
> >
> >
> > On 19.07.2018 17:49, Josef Bacik wrote:
> > > If we're allocating a new space cache inode it's likely going to be
> > > under a transaction handle, so we need to use GFP_NOFS to keep from
> > > deadlocking. Otherwise GFP_KERNEL is fine.
> > >
> > > Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > > ---
> > > fs/btrfs/free-space-cache.c | 5 +++++
> > > fs/btrfs/inode.c | 3 ++-
> > > fs/btrfs/transaction.h | 1 +
> > > 3 files changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> > > index d5f80cb300be..13bc514e4e16 100644
> > > --- a/fs/btrfs/free-space-cache.c
> > > +++ b/fs/btrfs/free-space-cache.c
> > > @@ -68,7 +68,12 @@ static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
> > > btrfs_disk_key_to_cpu(&location, &disk_key);
> > > btrfs_release_path(path);
> > >
> > > + /* We need this set so that we use GFP_NOFS when allocating our inode. */
> > > + if (current->journal_info == NULL)
> > > + current->journal_info = BTRFS_TRANS_STUB;
> > > inode = btrfs_iget(fs_info->sb, &location, root, NULL);
> > > + if (current->journal_info == BTRFS_TRANS_STUB)
> > > + current->journal_info = NULL;
> > This is not safe in the face of stacked filesystem, i.e ext4 uses the
> > journal_info.
> >
> > > if (IS_ERR(inode))
> > > return inode;
> > > if (is_bad_inode(inode)) {
> > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > > index eba61bcb9bb3..14ecfe5d6110 100644
> > > --- a/fs/btrfs/inode.c
> > > +++ b/fs/btrfs/inode.c
> > > @@ -9211,8 +9211,9 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
> > > struct btrfs_fs_info *fs_info = btrfs_sb(sb);
> > > struct btrfs_inode *ei;
> > > struct inode *inode;
> > > + gfp_t flags = (current->journal_info) ? GFP_NOFS : GFP_KERNEL;
> > >
> > > - ei = kmem_cache_alloc(btrfs_inode_cachep, GFP_KERNEL);
> > > + ei = kmem_cache_alloc(btrfs_inode_cachep, flags);
> >
> > Why don't you just hardcode GFP_NOFS? We should be striving at removing
> > abuse of ->journal_info than proliferating it.
>
> We're also removing unnecessary use of GFP_NOFS. The right way here is
> to use memalloc_nofs_save/memalloc_nofs_restore around btrfs_iget.
Huh I didn't know this existed, that's neat. I'll change this patch to do that,
thanks,
Josef
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