filemap_get_folio can return NULL, so exit early for that case.
Signed-off-by: Christoph Hellwig <[email protected]>
---
fs/gfs2/lops.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 1902413d5d123e..51d4b610127cdb 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -472,6 +472,8 @@ static void gfs2_jhead_process_page(struct gfs2_jdesc *jd, unsigned long index,
struct folio *folio;
folio = filemap_get_folio(jd->jd_inode->i_mapping, index);
+ if (!folio)
+ return;
folio_wait_locked(folio);
if (folio_test_error(folio))
--
2.39.0
On Wed, Jan 18, 2023 at 10:43:27AM +0100, Christoph Hellwig wrote:
> filemap_get_folio can return NULL, so exit early for that case.
I'm not sure it can return NULL in this specific case. As I understand
this code, we're scanning the journal looking for the log head. We've
just submitted the bio to read this page. I suppose memory pressure
could theoretically push the page out, but if it does, we're doing the
wrong thing by just returning here; we need to retry reading the page.
Assuming we're not willing to do the work to add that case, I think I'd
rather see the crash in folio_wait_locked() than get data corruption
from failing to find the head of the log.
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> fs/gfs2/lops.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
> index 1902413d5d123e..51d4b610127cdb 100644
> --- a/fs/gfs2/lops.c
> +++ b/fs/gfs2/lops.c
> @@ -472,6 +472,8 @@ static void gfs2_jhead_process_page(struct gfs2_jdesc *jd, unsigned long index,
> struct folio *folio;
>
> folio = filemap_get_folio(jd->jd_inode->i_mapping, index);
> + if (!folio)
> + return;
>
> folio_wait_locked(folio);
> if (folio_test_error(folio))
> --
> 2.39.0
>
[Christoph's email ended up in my spam folder; I hope that was a
one-time-only occurrence.]
On Wed, Jan 18, 2023 at 5:00 PM Matthew Wilcox <[email protected]> wrote:
> On Wed, Jan 18, 2023 at 10:43:27AM +0100, Christoph Hellwig wrote:
> > filemap_get_folio can return NULL, so exit early for that case.
>
> I'm not sure it can return NULL in this specific case. As I understand
> this code, we're scanning the journal looking for the log head. We've
> just submitted the bio to read this page. I suppose memory pressure
> could theoretically push the page out, but if it does, we're doing the
> wrong thing by just returning here; we need to retry reading the page.
>
> Assuming we're not willing to do the work to add that case, I think I'd
> rather see the crash in folio_wait_locked() than get data corruption
> from failing to find the head of the log.
>
> > Signed-off-by: Christoph Hellwig <[email protected]>
> > ---
> > fs/gfs2/lops.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
> > index 1902413d5d123e..51d4b610127cdb 100644
> > --- a/fs/gfs2/lops.c
> > +++ b/fs/gfs2/lops.c
> > @@ -472,6 +472,8 @@ static void gfs2_jhead_process_page(struct gfs2_jdesc *jd, unsigned long index,
> > struct folio *folio;
> >
> > folio = filemap_get_folio(jd->jd_inode->i_mapping, index);
> > + if (!folio)
> > + return;
We're actually still holding a reference to the folio from the
find_or_create_page() in gfs2_find_jhead() here, so we know that
memory pressure can't push the page out and filemap_get_folio() won't
return NULL.
> >
> > folio_wait_locked(folio);
> > if (folio_test_error(folio))
> > --
> > 2.39.0
> >
>
Thanks,
Andreas
On Wed, Jan 18, 2023 at 05:24:32PM +0100, Andreas Gruenbacher wrote:
> We're actually still holding a reference to the folio from the
> find_or_create_page() in gfs2_find_jhead() here, so we know that
> memory pressure can't push the page out and filemap_get_folio() won't
> return NULL.
Ok, I'll drop this patch.