Messages in this thread | | | Date | Sat, 20 Sep 2003 19:36:26 +0400 | From | Andrew Zabolotny <> | Subject | __make_request() bug and a fix variant |
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On Sat, 20 Sep 2003 13:37:37 +0200 Jens Axboe <axboe@suse.de> wrote:
> I dunno if you were the one posting this issue here some months ago? No, it wasn't me :-)
> Show me a regular kernel path that passes invalid b_reqnext to > __make_request? That would be a bug, indeed, but I've never heard of > such a bug. Most likely it's a bug in your driver, not initialising > b_reqnext. I have been calling bread() which was causing me troubles. bread does not accept a buffer_head from outside, it gets a new one and returns it. So I don't have any control over b_reqnext field - the bug happens inside bread() between these lines:
bh = getblk(dev, block, size); /* here bh_reqnext is already junk. In fact, I partially solved this problem by making my own clone of bread() and setting b_reqnext to NULL right here. But unfortunately, there is no guarantee we'll fix all invalid buffer_heads - maybe some remain in the pool and will be returned to other innocent drivers requesting them. */ if (buffer_uptodate(bh)) return bh; /* and now ll_rw_block will try to merge the bh with those already in the queue, and if it will take the ELEVATOR_NO_MERGE path, bh_reqnext will still remain junk. */ ll_rw_block(READ, 1, &bh);
> You can see the initialisor for buffer_heads is > init_buffer_head, which memsets the entire buffer_head. When a > buffer_head is detached from the request list, b_reqnext is cleared > too. Ah, so I was correct that __make_request expects b_reqnext to be already set to NULL. In this case the bug should be somewhere else - in some code that returns buffer_head's back to the pool of buffers.
Interesting that right before the driver crashes in bread() I call grok_partitions. I think the bug is somewhere there. I will do a new debug session at Monday (the code that breaks is at work), so I will post new details if I find any.
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