On Tue, 4 Sep 2012, J. Bruce Fields wrote:
> Date: Tue, 4 Sep 2012 10:52:13 -0400
> From: J. Bruce Fields <bfields@xxxxxxxxxxxx>
> To: Lukas Czerner <lczerner@xxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, tytso@xxxxxxx,
> hughd@xxxxxxxxxx, linux-mm@xxxxxxxxx
> Subject: Re: [PATCH 02/15 v2] jbd2: implement
> jbd2_journal_invalidatepage_range
>
> On Fri, Aug 31, 2012 at 06:21:38PM -0400, Lukas Czerner wrote:
> > mm now supports invalidatepage_range address space operation and there
> > are two file system using jbd2 also implementing punch hole feature
> > which can benefit from this. We need to implement the same thing for
> > jbd2 layer in order to allow those file system take benefit of this
> > functionality.
> >
> > With new function jbd2_journal_invalidatepage_range() we can now specify
> > length to invalidate, rather than assuming invalidate to the end of the
> > page.
> >
> > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > ---
> > fs/jbd2/journal.c | 1 +
> > fs/jbd2/transaction.c | 19 +++++++++++++++++--
> > include/linux/jbd2.h | 2 ++
> > 3 files changed, 20 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> > index e149b99..e4618e9 100644
> > --- a/fs/jbd2/journal.c
> > +++ b/fs/jbd2/journal.c
> > @@ -86,6 +86,7 @@ EXPORT_SYMBOL(jbd2_journal_force_commit_nested);
> > EXPORT_SYMBOL(jbd2_journal_wipe);
> > EXPORT_SYMBOL(jbd2_journal_blocks_per_page);
> > EXPORT_SYMBOL(jbd2_journal_invalidatepage);
> > +EXPORT_SYMBOL(jbd2_journal_invalidatepage_range);
> > EXPORT_SYMBOL(jbd2_journal_try_to_free_buffers);
> > EXPORT_SYMBOL(jbd2_journal_force_commit);
> > EXPORT_SYMBOL(jbd2_journal_file_inode);
> > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> > index fb1ab953..65c1374 100644
> > --- a/fs/jbd2/transaction.c
> > +++ b/fs/jbd2/transaction.c
> > @@ -1993,10 +1993,20 @@ zap_buffer_unlocked:
> > *
> > */
> > void jbd2_journal_invalidatepage(journal_t *journal,
> > - struct page *page,
> > - unsigned long offset)
> > + struct page *page,
> > + unsigned long offset)
> > +{
> > + jbd2_journal_invalidatepage_range(journal, page, offset,
> > + PAGE_CACHE_SIZE - offset);
> > +}
> > +
> > +void jbd2_journal_invalidatepage_range(journal_t *journal,
> > + struct page *page,
> > + unsigned int offset,
> > + unsigned int length)
> > {
> > struct buffer_head *head, *bh, *next;
> > + unsigned int stop = offset + length;
> > unsigned int curr_off = 0;
> > int may_free = 1;
> >
> > @@ -2005,6 +2015,8 @@ void jbd2_journal_invalidatepage(journal_t *journal,
> > if (!page_has_buffers(page))
> > return;
> >
> > + BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);
>
> This misses e.g. length == (unsigned int)(-1), offset = 1. Could make
> it obvious with:
Hmm.. So if length = -1 (e.g. UINT_MAX) and offset = 1 then:
offset + length = 0
so
length is bigger than (offset + length) right ? Speaking in numbers:
length = 4294967295
offset = 1
stop = length + offset = 0
so (0 < 4294967295) is true and we'll BUG() on this, right ?
Am I missing something ?
-Lukas
>
> BUG_ON(offset > PAGE_CACHE_SIZE || length > PAGE_CACHE_SIZE);
> BUG_ON(stop > PAGE_CACHE_SIZE);
>
> Or is that overkill?
>
> --b.
>
> > +
> > /* We will potentially be playing with lists other than just the
> > * data lists (especially for journaled data mode), so be
> > * cautious in our locking. */
> > @@ -2014,6 +2026,9 @@ void jbd2_journal_invalidatepage(journal_t *journal,
> > unsigned int next_off = curr_off + bh->b_size;
> > next = bh->b_this_page;
> >
> > + if (next_off > stop)
> > + return;
> > +
> > if (offset <= curr_off) {
> > /* This block is wholly outside the truncation point */
> > lock_buffer(bh);
> > diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> > index 3efc43f..21288fa 100644
> > --- a/include/linux/jbd2.h
> > +++ b/include/linux/jbd2.h
> > @@ -1101,6 +1101,8 @@ extern int jbd2_journal_forget (handle_t *, struct buffer_head *);
> > extern void journal_sync_buffer (struct buffer_head *);
> > extern void jbd2_journal_invalidatepage(journal_t *,
> > struct page *, unsigned long);
> > +extern void jbd2_journal_invalidatepage_range(journal_t *, struct page *,
> > + unsigned int, unsigned int);
> > extern int jbd2_journal_try_to_free_buffers(journal_t *, struct page *, gfp_t);
> > extern int jbd2_journal_stop(handle_t *);
> > extern int jbd2_journal_flush (journal_t *);
> > --
> > 1.7.7.6
> >
> > --
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