RE: 2.6.21-mm1

Williams, Dan J
2007-05-06T22:01:37Z

> From: Andrew Morton [mailto:akpm@linux-foundation.org]
> On Sun, 6 May 2007 22:44:29 +0200 Sam Ravnborg <sam@ravnborg.org>
wrote:
>
> > On Sun, May 06, 2007 at 08:33:48AM +0400, Dan Kruchinin wrote:
> > > >
> > >
>
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21/2.6
.21-
> mm1/
> > >
> > > I have the following message after kernel compilation:
> > >
> > > ---
> > > ...
> > > WARNING: init/built-in.o - Section mismatch: reference to
.init.text:
> > > from .text between 'rest_init' (at offset 0x11e) and 'try_name'
> >
> > Covered in another mail.
> >
> > > ...
> > > ...
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x20)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x24)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x28)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x2c)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x30)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x34)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x38)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x3c)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x40)
> > > WARNING: drivers/dma/async_tx.o - Section mismatch: reference to
> > > .init.data: from .data after 'channel_table' (at offset 0x44)
> >
> > We have following code:
> > /* guarantee that calls that happen before init will not find a
channel */
> > static struct chan_ref_percpu __initdata null_chan_ref[NR_CPUS];
> >
> > static struct chan_ref_percpu *channel_table[] = {
> > DMA_TX_ARRAY_INIT(null_chan_ref)
> > };
> >
> > The DMA_TX_ARRAY_INIT is some macro obscufation that serves no
> > real use and just hide a few assignements.
> > What happens here is that we assign channel_table a value
> > that are used as cover-up until the real assignment happens
> > in the init function.
> > So the only real way to fix this seems to remove the otherwise
correct
> > __initdata mark on null_chan_ref.
> > Thats one pointer wasted pr. cpu (in total NR_CPUS).
> >
>
> (add Dan to cc)

Not sure if there is a better way to do this, but I went ahead and added
a global flag that gets set after init. It also lets DMA_TX_ARRAY_INIT
go away, but it adds another branch to the fast path.

I rebased "git://lost.foo-projects.org/~dwillia2/git/iop md-accel-linus"
with the following:

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index f2d8b75..95a87a0 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -76,27 +76,12 @@ enum dma_transaction_type {
DMA_PQ_ZERO_SUM,
DMA_MEMSET,
DMA_MEMCPY_CRC32C,
- DMA_INTERRUPT, /* when updating, make this the last entry and
- * update the DMA_TX_ARRAY_INIT macro
- */
+ DMA_INTERRUPT, /* when updating, make this the last entry */
};

/* last transaction type for creation of the capabilities mask */
#define DMA_TX_TYPE_END (DMA_INTERRUPT + 1)

-/* helper macro for clients defining transaction arrays */
-#define DMA_TX_ARRAY_INIT(x) \
- [DMA_MEMCPY] = x, \
- [DMA_XOR] = x, \
- [DMA_PQ_XOR] = x, \
- [DMA_DUAL_XOR] = x, \
- [DMA_PQ_UPDATE] = x, \
- [DMA_ZERO_SUM] = x, \
- [DMA_PQ_ZERO_SUM] = x, \
- [DMA_MEMSET] = x, \
- [DMA_MEMCPY_CRC32C] = x,\
- [DMA_INTERRUPT] = x,
-
/**
* dma_cap_mask_t - capabilities bitmap modeled after cpumask_t.
* See linux/cpumask.h
diff --git a/drivers/dma/async_tx.c b/drivers/dma/async_tx.c
index 6bbbacc..6450cfd 100644
--- a/drivers/dma/async_tx.c
+++ b/drivers/dma/async_tx.c
@@ -52,12 +52,8 @@ struct chan_ref_percpu {
struct dma_chan_ref *ref;
};

-/* guarantee that calls that happen before init will not find a channel
*/
-static struct chan_ref_percpu __initdata null_chan_ref[NR_CPUS];
-
-static struct chan_ref_percpu *channel_table[] = {
- DMA_TX_ARRAY_INIT(null_chan_ref)
-};
+static int channel_table_initialized;
+static struct chan_ref_percpu *channel_table[DMA_TX_TYPE_END];

/**
* async_tx_lock - protect modification of async_tx_master_list and
serialize
@@ -260,6 +256,7 @@ async_tx_init(void)

dma_async_client_register(&async_tx_dma);
dma_async_client_chan_request(&async_tx_dma);
+ channel_table_initialized = 1;

printk("async_tx: api initialized (async)\n");

@@ -309,13 +306,14 @@ async_tx_find_channel(struct
dma_async_tx_descriptor *depend_tx,
if (depend_tx &&
dma_has_cap(tx_type, depend_tx->chan->device->cap_mask))
return depend_tx->chan;
- else {
+ else if (likely(channel_table_initialized)) {
struct dma_chan_ref *ref;
int cpu = get_cpu();
ref = per_cpu_ptr(channel_table[tx_type], cpu)->ref;
put_cpu();
return ref ? ref->chan : NULL;
- }
+ } else
+ return NULL;
}
#else
static int __init async_tx_init(void)