Messages in this thread | | | Date | Tue, 30 Jul 2002 17:44:00 -0300 (BRT) | From | Marcelo Tosatti <> | Subject | Re: [patch] disable READA |
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Ah, haven't read the full message.
Forget about my question. :)
On Tue, 30 Jul 2002, Marcelo Tosatti wrote:
> > Who is using READA this days ? > > > On Tue, 30 Jul 2002, Andrew Morton wrote: > > > > > There's a bug in bread() which can cause it to misinterpret a > > failed READA request as an IO error on SMP. > > > > If a filesytem block is subject to READA and __make_request() > > decides that the request would block then __make_request() > > will (via end_buffer_io_sync) mark the buffer as not uptodate > > and will unlock it. > > > > But if another CPU attempts to bread() the same buffer at the same > > time, the following happens: > > > > 1: ll_rw_block() sees the buffer is locked and does nothing at all > > > > 2: bread() does a wait_on_buffer() > > > > 3: the other CPU (the one doing READA) unlocks the non uptodate buffer > > > > 4: bread() sees the buffer come unlocked. It's not uptodate, so > > bread() bogusly reports an IO error. > > > > I haven't seen it in the wild, because it is rare to get that > > much read I/O in flight. reiserfs and ext3 (at least) use READA. > > > > An appropriate fix for 2.4 is to disable READA. > > > > > > ll_rw_blk.c | 2 ++ > > 1 files changed, 2 insertions > > > > --- 2.4.19-rc3/drivers/block/ll_rw_blk.c~no-readahead Tue Jul 30 14:18:17 2002 > > +++ 2.4.19-rc3-akpm/drivers/block/ll_rw_blk.c Tue Jul 30 14:19:52 2002 > > @@ -841,7 +841,9 @@ static int __make_request(request_queue_ > > rw_ahead = 0; /* normal case; gets changed below for READA */ > > switch (rw) { > > case READA: > > +#if 0 /* bread() misinterprets failed READA attempts as IO errors on SMP */ > > rw_ahead = 1; > > +#endif > > rw = READ; /* drop into READ */ > > case READ: > > case WRITE:
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