When I was cut and pasting to the email I grabbed the wrong code. In
the end asynch callbacks, replace b_next_free with d_dev_id -- and it
still crashes.
Jeff
"Jeff V. Merkey" wrote:
>
> I have tried all sorts of stuff to make the swapper Ooops go away. I
> have also completely reviewed all of the mm code, fs code, etc, etc.
> And here's what I think I've determined to be invalid in my assumptions
> about what's there:
>
> 1. Linux 2.2.15 and 2.3.99 do not support true Asynch IO. Asynch IO
> allows a caller to post a very large number of requests, is not **NOT**
> polled, and should be interrupt driven. The first request should "kick"
> the queue head into the driver, then the driver should feed the next
> buffer on the IO completion interrupt until the queue head is empty.
> The way it's implemented in Linux requires that the bottom half ISR be
> "polled" within wait_on_buffer() or some other function to initiate the
> I/O and block until the IO returns -- how is this asynchronous I/O.
>
> 2. While the semantics appear to be Asynch, the interface is actually
> synchronous in behavior -- you have to poll the drives after posting IO
> to start the disks. The dependency on the lock_kernel() call on 2.2.15
> guarantees that most callers will block when attempting multiple calls
> to ll_rw_blk(), so there went the parallelism. I have noticed that if I
> hold the kernel lock over the I/O (which is what is happening in
> filemap.c and buffer.c) then the swapper does not crash the system.
> This means that all I/O requests performed are really synchronous since
> only one caller seems to be able to post at one time with crashing.
>
> 3. Feeding more than a handful of requests at one time to THE LINUX
> BUFFER CACHE (forget NWFS code - I tried this with just Linux) will
> cause the swapper process to Ooops and die. I implemented some very
> simple code that just calls the buffer cache and tries to do asynch I/O
> and "**KAPOW!!!*** , the system crashes. The code is attached.
>
> Jeff Merkey
> CEO, TRG
>
> ------------------------------------------------------------------------
> Name: aio.c
> aio.c Type: Notepad File (application/x-unknown-content-type-cfile)
> Encoding: base64
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