Linux 2.6.x : cpm_dpalloc alignment bug perhaps not fully resolved

[Laurent Lagrange]

Hello Pantelis,

Few months ago (25 January 2006), I sent a mail about an alignment bug in
cpm_dpalloc.
I applied and verified the provided patch. I was very satisfied with the
result.

Today I port a driver from Linux 2.4 to Linux 2.6 and I have strange
results.

The driver allocates rx and tx bds (8 bytes aligned) in the module_init for
4 SCC ports.
That is always right. Then one port is opened by an application and a user
configuration
is set via an ioctl (set_conf).

This ioctl first frees the old bds :
	cpm_dpfree(chan->rx_bd_offset);
	cpm_dpfree(chan->tx_bd_offset);
then allocates the new ones :
	chan->rx_bd_offset = cpm_dpalloc(sizeof(cbd_t) * chan->conf.rx_bufnbr, 8);
	chan->tx_bd_offset = cpm_dpalloc(sizeof(cbd_t) * chan->conf.tx_bufnbr, 8);
with rx_bufnbr == 8 and tx_bufnbr == 2

module_init
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8
SCC2 rx_bd_offset=1c0
SCC2 tx_bd_offset=208
SCC3 rx_bd_offset=220
SCC3 tx_bd_offset=260
SCC4 rx_bd_offset=278
SCC4 tx_bd_offset=2c0
set_conf
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a4	-> ???

module_init
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8
SCC2 rx_bd_offset=1c0
SCC2 tx_bd_offset=208
SCC3 rx_bd_offset=220
SCC3 tx_bd_offset=260
SCC4 rx_bd_offset=278
SCC4 tx_bd_offset=2c0
set_conf
SCC2 rx_bd_offset=1c0
SCC2 tx_bd_offset=202	-> ???

module_init
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8
SCC2 rx_bd_offset=1c0
SCC2 tx_bd_offset=208
SCC3 rx_bd_offset=220
SCC3 tx_bd_offset=260
SCC4 rx_bd_offset=278
SCC4 tx_bd_offset=2c0
set_conf
SCC3 rx_bd_offset=220
SCC3 tx_bd_offset=260	-> ok

module_init
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8
SCC2 rx_bd_offset=1c0
SCC2 tx_bd_offset=208
SCC3 rx_bd_offset=220
SCC3 tx_bd_offset=260
SCC4 rx_bd_offset=278
SCC4 tx_bd_offset=2c0
set_conf
SCC4 rx_bd_offset=278
SCC4 tx_bd_offset=2c0	-> ok

WARNING : if I only uses the SCC1 port without allocating bds for the other
ports,
I can free and reallocate the bds for the SCC1 port as many times I want.

module_init
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8
set_conf
SCC1 rx_bd_offset=160
SCC1 tx_bd_offset=1a8	-> ok

Really, I don't understand how this can arise.
Any idea ?

Thanks
Laurent