Messages in this thread | | | Date | Fri, 14 Sep 2012 19:18:47 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty() |
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On Fri, Sep 14, 2012 at 08:13:05PM +0900, OGAWA Hirofumi wrote: > OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes: > > > Fengguang Wu <fengguang.wu@intel.com> writes: > > > >> On Wed, Sep 12, 2012 at 03:28:42AM +0900, OGAWA Hirofumi wrote: > >>> > >>> If bdi has BDI_CAP_NO_WRITEBACK, bdi_forker_thread() doesn't start > >>> writeback thread. This means there is no consumer of work item made > >>> by bdi_queue_work(). > >>> > >>> This adds to checking of !bdi_cap_writeback_dirty(sb->s_bdi) before > >>> calling bdi_queue_work(), otherwise queued work never be consumed. > >>> > >>> Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> > >>> --- > >>> > >>> fs/fs-writeback.c | 7 +++++-- > >>> 1 file changed, 5 insertions(+), 2 deletions(-) > >>> > >>> diff -puN fs/fs-writeback.c~noop_backing_dev_info-check-fix fs/fs-writeback.c > >>> --- linux/fs/fs-writeback.c~noop_backing_dev_info-check-fix 2012-09-11 06:12:30.000000000 +0900 > >>> +++ linux-hirofumi/fs/fs-writeback.c 2012-09-11 06:12:30.000000000 +0900 > >>> @@ -120,6 +120,9 @@ __bdi_start_writeback(struct backing_dev > >>> { > >>> struct wb_writeback_work *work; > >>> > >>> + if (!bdi_cap_writeback_dirty(bdi)) > >>> + return; > >> > >> Will someone in the current kernel actually call > >> __bdi_start_writeback() on a BDI_CAP_NO_WRITEBACK bdi? > >> > >> If the answer is no, VM_BUG_ON(!bdi_cap_writeback_dirty(bdi)) looks better. > > > > I guess nobody call it in current kernel though. Hmm.., but we also have > > check in __mark_inode_dirty(), nobody should be using it, right? > > > > If we defined it as the bug, I can't see what BDI_CAP_NO_WRITEBACK wants > > to do actually. We are not going to allow to disable the writeback task? > > ping. > > You are saying we should change bdi_cap_writeback_dirty(bdi) to > VM_BUG_ON() too in __mark_inode_dirty()? And probably, you are going to > remove the usage of BDI_CAP_NO_WRITEBACK for sb->s_bdi?
No, I'm talking about this chunk only. My feeling is, adding the bdi_cap_writeback_dirty() detection in __bdi_start_writeback() sounds too late. If ever the test is false, it may well indicate a bug in the callers. Obviously the callers all assume success because __bdi_start_writeback() does not even return a value.
Thanks, Fengguang
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