| Message ID | 20201217011157.92549-5-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xfs: avoid transaction reservation recursion | expand |
On Thu, Dec 17, 2020 at 09:11:57AM +0800, Yafang Shao wrote: > PF_FSTRANS which is used to avoid transaction reservation recursion, is > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to > PF_MEMALLOC_NOFS") and replaced by PF_MEMALLOC_NOFS which means to avoid > filesystem reclaim recursion. > > As these two flags have different meanings, we'd better reintroduce > PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct, > we can reuse the current->journal_info to do that, per Willy. As the > check of transaction reservation recursion is used by XFS only, we can > move the check into xfs_vm_writepage(s), per Dave. > > Cc: Darrick J. Wong <darrick.wong@oracle.com> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org> > Cc: Christoph Hellwig <hch@lst.de> > Cc: Dave Chinner <david@fromorbit.com> > Cc: Michal Hocko <mhocko@kernel.org> > Cc: David Howells <dhowells@redhat.com> > Cc: Jeff Layton <jlayton@redhat.com> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > --- > fs/iomap/buffered-io.c | 7 ------- > fs/xfs/xfs_aops.c | 17 +++++++++++++++++ > fs/xfs/xfs_trans.h | 26 +++++++++++++++++++------- > 3 files changed, 36 insertions(+), 14 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index 10cc7979ce38..3c53fa6ce64d 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -1458,13 +1458,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data) > PF_MEMALLOC)) > goto redirty; > > - /* > - * Given that we do not allow direct reclaim to call us, we should > - * never be called in a recursive filesystem reclaim context. > - */ > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > - goto redirty; > - > /* > * Is this page beyond the end of the file? > * > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > index 2371187b7615..0da0242d42c3 100644 > --- a/fs/xfs/xfs_aops.c > +++ b/fs/xfs/xfs_aops.c > @@ -568,6 +568,16 @@ xfs_vm_writepage( > { > struct xfs_writepage_ctx wpc = { }; > > + /* > + * Given that we do not allow direct reclaim to call us, we should > + * never be called while in a filesystem transaction. > + */ Comment is wrong. This is not protecting against direct reclaim recursion, this is protecting against writeback from within a transaction context. Best to remove the comment altogether, because it is largely redundant. > + if (WARN_ON_ONCE(xfs_trans_context_active())) { > + redirty_page_for_writepage(wbc, page); > + unlock_page(page); > + return 0; > + } > + > return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops); > } > > @@ -579,6 +589,13 @@ xfs_vm_writepages( > struct xfs_writepage_ctx wpc = { }; > > xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED); > + /* > + * Given that we do not allow direct reclaim to call us, we should > + * never be called while in a filesystem transaction. > + */ same here. > + if (WARN_ON_ONCE(xfs_trans_context_active())) > + return 0; > + > return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops); > } > > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h > index 12380eaaf7ce..0c8140147b9b 100644 > --- a/fs/xfs/xfs_trans.h > +++ b/fs/xfs/xfs_trans.h > @@ -268,29 +268,41 @@ xfs_trans_item_relog( > return lip->li_ops->iop_relog(lip, tp); > } > > +static inline bool > +xfs_trans_context_active(void) > +{ > + /* Use journal_info to indicate current is in a transaction */ > + return current->journal_info != NULL; > +} Comment is not necessary. > + > static inline void > xfs_trans_context_set(struct xfs_trans *tp) > { > + ASSERT(!current->journal_info); > + current->journal_info = tp; > tp->t_pflags = memalloc_nofs_save(); > } > > static inline void > xfs_trans_context_clear(struct xfs_trans *tp) > { > + /* > + * If xfs_trans_context_swap() handed the NOFS context to a > + * new transaction we do not clear the context here. > + */ It's a transaction context, not a "NOFS context". Setting NOFS is just something we implement inside the transaction context. More correct would be: /* * If we handed over the context via xfs_trans_context_swap() then * the context is no longer ours to clear. */ Cheers, Dave.
On Fri, Dec 18, 2020 at 8:14 AM Dave Chinner <david@fromorbit.com> wrote: > > On Thu, Dec 17, 2020 at 09:11:57AM +0800, Yafang Shao wrote: > > PF_FSTRANS which is used to avoid transaction reservation recursion, is > > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to > > PF_MEMALLOC_NOFS") and replaced by PF_MEMALLOC_NOFS which means to avoid > > filesystem reclaim recursion. > > > > As these two flags have different meanings, we'd better reintroduce > > PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct, > > we can reuse the current->journal_info to do that, per Willy. As the > > check of transaction reservation recursion is used by XFS only, we can > > move the check into xfs_vm_writepage(s), per Dave. > > > > Cc: Darrick J. Wong <darrick.wong@oracle.com> > > Cc: Matthew Wilcox (Oracle) <willy@infradead.org> > > Cc: Christoph Hellwig <hch@lst.de> > > Cc: Dave Chinner <david@fromorbit.com> > > Cc: Michal Hocko <mhocko@kernel.org> > > Cc: David Howells <dhowells@redhat.com> > > Cc: Jeff Layton <jlayton@redhat.com> > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > > --- > > fs/iomap/buffered-io.c | 7 ------- > > fs/xfs/xfs_aops.c | 17 +++++++++++++++++ > > fs/xfs/xfs_trans.h | 26 +++++++++++++++++++------- > > 3 files changed, 36 insertions(+), 14 deletions(-) > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > index 10cc7979ce38..3c53fa6ce64d 100644 > > --- a/fs/iomap/buffered-io.c > > +++ b/fs/iomap/buffered-io.c > > @@ -1458,13 +1458,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data) > > PF_MEMALLOC)) > > goto redirty; > > > > - /* > > - * Given that we do not allow direct reclaim to call us, we should > > - * never be called in a recursive filesystem reclaim context. > > - */ > > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > > - goto redirty; > > - > > /* > > * Is this page beyond the end of the file? > > * > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > index 2371187b7615..0da0242d42c3 100644 > > --- a/fs/xfs/xfs_aops.c > > +++ b/fs/xfs/xfs_aops.c > > @@ -568,6 +568,16 @@ xfs_vm_writepage( > > { > > struct xfs_writepage_ctx wpc = { }; > > > > + /* > > + * Given that we do not allow direct reclaim to call us, we should > > + * never be called while in a filesystem transaction. > > + */ > > Comment is wrong. This is not protecting against direct reclaim > recursion, this is protecting against writeback from within a > transaction context. > Ah, I forgot to change this comment after copy and paste. Thanks for pointing it out. > Best to remove the comment altogether, because it is largely > redundant. > Sure, I will remove these comments. > > + if (WARN_ON_ONCE(xfs_trans_context_active())) { > > + redirty_page_for_writepage(wbc, page); > > + unlock_page(page); > > + return 0; > > + } > > + > > return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops); > > } > > > > @@ -579,6 +589,13 @@ xfs_vm_writepages( > > struct xfs_writepage_ctx wpc = { }; > > > > xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED); > > + /* > > + * Given that we do not allow direct reclaim to call us, we should > > + * never be called while in a filesystem transaction. > > + */ > > same here. > > > + if (WARN_ON_ONCE(xfs_trans_context_active())) > > + return 0; > > + > > return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops); > > } > > > > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h > > index 12380eaaf7ce..0c8140147b9b 100644 > > --- a/fs/xfs/xfs_trans.h > > +++ b/fs/xfs/xfs_trans.h > > @@ -268,29 +268,41 @@ xfs_trans_item_relog( > > return lip->li_ops->iop_relog(lip, tp); > > } > > > > +static inline bool > > +xfs_trans_context_active(void) > > +{ > > + /* Use journal_info to indicate current is in a transaction */ > > + return current->journal_info != NULL; > > +} > > Comment is not necessary. > > > + > > static inline void > > xfs_trans_context_set(struct xfs_trans *tp) > > { > > + ASSERT(!current->journal_info); > > + current->journal_info = tp; > > tp->t_pflags = memalloc_nofs_save(); > > } > > > > static inline void > > xfs_trans_context_clear(struct xfs_trans *tp) > > { > > + /* > > + * If xfs_trans_context_swap() handed the NOFS context to a > > + * new transaction we do not clear the context here. > > + */ > > It's a transaction context, not a "NOFS context". Setting NOFS is > just something we implement inside the transaction context. More > correct would be: > > /* > * If we handed over the context via xfs_trans_context_swap() then > * the context is no longer ours to clear. > */ > Sure, I will change it.
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 10cc7979ce38..3c53fa6ce64d 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -1458,13 +1458,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data) PF_MEMALLOC)) goto redirty; - /* - * Given that we do not allow direct reclaim to call us, we should - * never be called in a recursive filesystem reclaim context. - */ - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) - goto redirty; - /* * Is this page beyond the end of the file? * diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index 2371187b7615..0da0242d42c3 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -568,6 +568,16 @@ xfs_vm_writepage( { struct xfs_writepage_ctx wpc = { }; + /* + * Given that we do not allow direct reclaim to call us, we should + * never be called while in a filesystem transaction. + */ + if (WARN_ON_ONCE(xfs_trans_context_active())) { + redirty_page_for_writepage(wbc, page); + unlock_page(page); + return 0; + } + return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops); } @@ -579,6 +589,13 @@ xfs_vm_writepages( struct xfs_writepage_ctx wpc = { }; xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED); + /* + * Given that we do not allow direct reclaim to call us, we should + * never be called while in a filesystem transaction. + */ + if (WARN_ON_ONCE(xfs_trans_context_active())) + return 0; + return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops); } diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h index 12380eaaf7ce..0c8140147b9b 100644 --- a/fs/xfs/xfs_trans.h +++ b/fs/xfs/xfs_trans.h @@ -268,29 +268,41 @@ xfs_trans_item_relog( return lip->li_ops->iop_relog(lip, tp); } +static inline bool +xfs_trans_context_active(void) +{ + /* Use journal_info to indicate current is in a transaction */ + return current->journal_info != NULL; +} + static inline void xfs_trans_context_set(struct xfs_trans *tp) { + ASSERT(!current->journal_info); + current->journal_info = tp; tp->t_pflags = memalloc_nofs_save(); } static inline void xfs_trans_context_clear(struct xfs_trans *tp) { + /* + * If xfs_trans_context_swap() handed the NOFS context to a + * new transaction we do not clear the context here. + */ + if (current->journal_info != tp) + return; + + current->journal_info = NULL; memalloc_nofs_restore(tp->t_pflags); } static inline void xfs_trans_context_swap(struct xfs_trans *tp, struct xfs_trans *ntp) { + ASSERT(current->journal_info == tp); + current->journal_info = ntp; ntp->t_pflags = tp->t_pflags; - /* - * For the rolling transaction, we have to set NOFS in the old - * transaction's t_pflags so that when we clear the context on - * the old transaction we don't actually change the thread's NOFS - * state. - */ - tp->t_pflags = current->flags | PF_MEMALLOC_NOFS; } #endif /* __XFS_TRANS_H__ */
PF_FSTRANS which is used to avoid transaction reservation recursion, is dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to PF_MEMALLOC_NOFS") and replaced by PF_MEMALLOC_NOFS which means to avoid filesystem reclaim recursion. As these two flags have different meanings, we'd better reintroduce PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct, we can reuse the current->journal_info to do that, per Willy. As the check of transaction reservation recursion is used by XFS only, we can move the check into xfs_vm_writepage(s), per Dave. Cc: Darrick J. Wong <darrick.wong@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Dave Chinner <david@fromorbit.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: David Howells <dhowells@redhat.com> Cc: Jeff Layton <jlayton@redhat.com> Signed-off-by: Yafang Shao <laoar.shao@gmail.com> --- fs/iomap/buffered-io.c | 7 ------- fs/xfs/xfs_aops.c | 17 +++++++++++++++++ fs/xfs/xfs_trans.h | 26 +++++++++++++++++++------- 3 files changed, 36 insertions(+), 14 deletions(-)