Messages in this thread |  | | Date | Thu, 8 May 2003 08:29:42 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] fixes for linked list bugs in block I/O code |
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On Wed, May 07 2003, Dave Peterson wrote: > I found a couple of small linked list bugs in __make_request() in > drivers/block/ll_rw_blk.c. The bugs exist in both kernels > 2.4.20 and 2.5.69. Therefore I have made patches for both > kernels. The problem is that when inserting a new buffer_head > into the linked list of buffer_head structures maintained by > "struct request", the b_reqnext field is not initialized. > > -Dave Peterson > dsp@llnl.gov > > > ========== START OF 2.4.20 PATCH FOR drivers/block/ll_rw_blk.c =========== > --- ll_rw_blk.c.old Wed May 7 15:54:58 2003 > +++ ll_rw_blk.c.new Wed May 7 15:58:07 2003 > @@ -973,6 +973,7 @@ > insert_here = &req->queue; > break; > } > + bh->b_reqnext = req->bhtail->b_reqnext;
This is convoluted nonsense, bhtail->b_reqnext is NULL by definition. So a simple
bh->b_reqnext = NULL;
is much clearer.
> req->bhtail->b_reqnext = bh; > req->bhtail = bh; > req->nr_sectors = req->hard_nr_sectors += count; > @@ -1061,6 +1062,7 @@ > req->waiting = NULL; > req->bh = bh; > req->bhtail = bh; > + bh->b_reqnext = NULL; > req->rq_dev = bh->b_rdev; > req->start_time = jiffies; > req_new_io(req, 0, count);
Bart already covered why 2.5 definitely does not need it. I dunno what to say for 2.4, to me it looks like a BUG if you pass in a buffer_head with uninitialized b_reqnext. Why should that member be any different?
In fact, from where did you see this buffer_head coming from? Who is submitting IO on a not properly inited bh? To me, that sounds like not a block layer bug but an fs bug.
-- Jens Axboe
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