On Fri, Apr 13, 2018 at 04:52:25PM -0700, Liu Bo wrote:
> On Fri, Apr 13, 2018 at 1:28 PM, Josef Bacik <josef@xxxxxxxxxxxxxx> wrote:
> > From: Josef Bacik <jbacik@xxxxxx>
> >
> > Since we're allocating under atomic we could every easily enomem, so if
> > that's the case and we can block then loop around and try to allocate
> > the prealloc not under a lock.
> >
> > We also saw this happen during try_to_release_page in production, in
> > which case it's completely valid to return ENOMEM so we can tell
> > try_to_release_page that we can't release this page.
> >
> > Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> > ---
> > fs/btrfs/extent_io.c | 28 ++++++++++++++++++++++++----
> > 1 file changed, 24 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> > index fb32394fd830..1054dc0158b5 100644
> > --- a/fs/btrfs/extent_io.c
> > +++ b/fs/btrfs/extent_io.c
> > @@ -593,8 +593,9 @@ int __clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> > struct extent_state *prealloc = NULL;
> > struct rb_node *node;
> > u64 last_end;
> > - int err;
> > + int err = 0;
> > int clear = 0;
> > + bool need_prealloc = false;
> >
> > btrfs_debug_check_extent_io_range(tree, start, end);
> >
> > @@ -617,6 +618,9 @@ int __clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> > * If we end up needing a new extent state we allocate it later.
> > */
> > prealloc = alloc_extent_state(mask);
> > + if (!prealloc && need_prealloc)
> > + return -ENOMEM;
> > + need_prealloc = false;
> > }
> >
> > spin_lock(&tree->lock);
> > @@ -676,7 +680,15 @@ int __clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> >
> > if (state->start < start) {
> > prealloc = alloc_extent_state_atomic(prealloc);
> > - BUG_ON(!prealloc);
> > + if (!prealloc) {
> > + if (gfpflags_allow_blocking(mask)) {
> > + need_prealloc = true;
> > + spin_unlock(&tree->lock);
> > + goto again;
>
> Could we simply 'goto search_again;' ?
>
We could, but I have another patch that's more involved that reworks this logic
and kills search_again, so I'm leaving it this way for now for this isolated
fix. Thanks,
Josef
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