> On Thu, 22 Feb 2007 08:42:26 +0100 Miklos Szeredi <[EMAIL PROTECTED]> wrote: > > > > > > Index: linux/mm/page-writeback.c > > > =================================================================== > > > --- linux.orig/mm/page-writeback.c 2007-02-19 17:32:41.000000000 > > > +0100 > > > +++ linux/mm/page-writeback.c 2007-02-19 18:05:28.000000000 +0100 > > > @@ -198,6 +198,25 @@ static void balance_dirty_pages(struct a > > > dirty_thresh) > > > break; > > > > > > + /* > > > + * Acquit this producer if there's little or nothing > > > + * to write back to this particular queue > > > + * > > > + * Without this check a deadlock is possible in the > > > + * following case: > > > + * > > > + * - filesystem A writes data through filesystem B > > > + * - filesystem A has dirty pages over dirty_thresh > > > + * - writeback is started, this triggers a write in B > > > + * - balance_dirty_pages() is called synchronously > > > + * - the write to B blocks > > > + * - the writeback completes, but dirty is still over threshold > > > + * - the blocking write prevents futher writes from happening > > > + */ > > > + if (atomic_long_read(&bdi->nr_dirty) + > > > + atomic_long_read(&bdi->nr_writeback) < 16) > > > + break; > > > + > > > > The problem seems to that little "- the write to B blocks". > > > > How come it blocks? I mean, if we cannot retire writes to that filesystem > > then we're screwed anyway. > > Sorry about the sloppy description. I mean, it's not the lowlevel > write that will block, but rather the VFS one > (generic_file_aio_write). It will block (or rather loop forever with > 0.1 second sleeps) in balance_dirty_pages(). That means, that for > this inode, i_mutex is held and no other writer can continue the work.
"this inode" I assume is the inode against filesystem A? Why does holding that inode's i_mutex prevent further writeback of pages in A? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
