Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 3 Sep 2003 08:40:57 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] ide task_map_rq() preempt count imbalance |
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On Wed, Sep 03 2003, Tejun Huh wrote: > Hello, > > 2.5 kernel continued to fail on my test machine with a lot of > scheduling while atomic messages. The offending function was > include/linux/ide.h:task_sectors() which calls task_map_rq() followed > by process_that_request_first(), taskfile_{input|output}_data() and > task_unmap_rq(). > > static inline void *task_map_rq(struct request *rq, unsigned long *flags) > { > /* > * fs request > */ > if (rq->cbio) > return rq_map_buffer(rq, flags); > > /* > * task request > */ > return rq->buffer + blk_rq_offset(rq); > } > > static inline void task_unmap_rq(struct request *rq, char *buffer, unsigned long *flags) > { > if (rq->cbio) > rq_unmap_buffer(buffer, flags); > } > > rq_[un]map_buffer() eventually call into k[un]map_atomic() which > adjust preempt_count(). The problem is that rq->cbio is cleared by > process_that_request_first() before calling task_unmap_rq(), so the > preempt_count() isn't decremented properly. > > As it seems that rq->cbio test is to avoid the cost of calling into > k[un]map_atomic, I just removed the optimization and it worked for me. > > I'm not familiar with ide and block layer. If I got something wrong, > please point out. > > -- > tejun > > # This is a BitKeeper generated patch for the following project: > # Project Name: Linux kernel tree > # This patch format is intended for GNU patch command version 2.5 or higher. > # This patch includes the following deltas: > # ChangeSet 1.1412 -> 1.1413 > # include/linux/ide.h 1.72 -> 1.73 > # > # The following is the BitKeeper ChangeSet Log > # -------------------------------------------- > # 03/09/03 tj@atj.dyndns.org 1.1413 > # - task_[un]map_rq() preempt count imbalance fixed. > # -------------------------------------------- > # > diff -Nru a/include/linux/ide.h b/include/linux/ide.h > --- a/include/linux/ide.h Wed Sep 3 14:50:20 2003 > +++ b/include/linux/ide.h Wed Sep 3 14:50:20 2003 > @@ -853,22 +853,12 @@ > > static inline void *task_map_rq(struct request *rq, unsigned long *flags) > { > - /* > - * fs request > - */ > - if (rq->cbio) > - return rq_map_buffer(rq, flags); > - > - /* > - * task request > - */ > - return rq->buffer + blk_rq_offset(rq); > + return rq_map_buffer(rq, flags); > } > > static inline void task_unmap_rq(struct request *rq, char *buffer, unsigned long *flags) > { > - if (rq->cbio) > - rq_unmap_buffer(buffer, flags); > + rq_unmap_buffer(buffer, flags); > } > > #endif /* !CONFIG_IDE_TASKFILE_IO */
This doesn't work, it's perfectly legit to use task_map_rq() on a non-bio backed request. You need to fix this differently.
-- Jens Axboe
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