Am Mittwoch, 23. Juni 2010 schrieb Lothar Wa?mann:

Hi,

quoted

we have a strange problem when booting from a Compact Flash card
as root-device. In one of 10 cases while booting an application from
root-filesystem dies with "Segmentation fault" without a visible error.
After booting the same application runs hundred times without error.
(we're talking about standard appl. like chat, pppd, hwclock and so on)

For debugging purposes we put printk's in kernels IDE driver 
and the problem disappeared. But replacing the printk by a usleep
or so (which is not a solution !) brings the problem back.
It seems that the application received faulty data from CF.
But how and why ?????????????????????????????

We tested with a custom PXA270 board with a CompactFlash in 
"true ide" on processor bus driven by "generic ide / pata_platform"
driver from linux-2.6.27.x.
(by the way linux-2.6.20.x showed the same problem).

Any ideas, hints, experiences, patches are very welcome :-)
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I guess that is the old cache problem that apparently was never really
fixed:
http://marc.info/?t=108537828400002&r=1&w=2

Hello
this hint was very helpful for understanding the problem.
In the mail from Russell King at 
<http://marc.info/?l=linux-arm-kernel&m=108611676807909&w=2>
he said : .... the rule is if the CPU writes to a page cache page,
it must call flush_dcache_page afterwards to ensure cache coherency with user space".

so i made the following patch in drivers/ide/ide-taskfile.c
in the function ide_pio_sector() where blocks from disk are read
into a cached page to apply the rule from Russell. 
===================================================================

--- ide-taskfile.c
+++ ide-taskfile.c.new

@@ -278,6 +278,7 @@
                hwif->tp_ops->input_data(drive, rq, buf, SECTOR_SIZE);

        kunmap_atomic(buf, KM_BIO_SRC_IRQ);
+       flush_dcache_page(page);
 #ifdef CONFIG_HIGHMEM
        local_irq_restore(flags);
 #endif

And from there on the problem disappeared :-))
What are you think about ???
Isn't this missing for years in IDE PIO driver ???
--------------------------------------------------------------
J?rgen Schindele  
Software-Entwicklung

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