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[PATCH v2] MIPS: Alchemy: fix dbdma ring destruction memory debugcheck.

To: Linux-MIPS <>
Subject: [PATCH v2] MIPS: Alchemy: fix dbdma ring destruction memory debugcheck.
From: Manuel Lauss <>
Date: Tue, 26 Jan 2010 20:39:33 +0100
Cc: Manuel Lauss <>
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DBDMA descriptors need to be located at 32-byte aligned addresses;
however kmalloc in conjunction with the SLAB allocator and 
CONFIG_DEBUG_SLUB enabled doesn't deliver any.  The dbdma code works
around that by allocating a larger area and realigning the start
address within it.

When freeing a channel however this adjustment is not taken into
account which results in an oops:

Kernel bug detected[#1]:
Call Trace:
[<80186010>] cache_free_debugcheck+0x284/0x318
[<801869d8>] kfree+0xe8/0x2a0
[<8010b31c>] au1xxx_dbdma_chan_free+0x2c/0x7c
[<80388dc8>] au1x_pcm_dbdma_free+0x34/0x4c
[<80388fa8>] au1xpsc_pcm_close+0x28/0x38
[<80383cb8>] soc_codec_close+0x14c/0x1cc
[<8036dbb4>] snd_pcm_release_substream+0x60/0xac
[<8036dc40>] snd_pcm_release+0x40/0xa0
[<8018c7a8>] __fput+0x11c/0x228
[<80188f60>] filp_close+0x7c/0x98
[<80189018>] sys_close+0x9c/0xe4
[<801022a0>] stack_done+0x20/0x3c

Fix this by recording the address delivered by kmalloc() and using
it as parameter to kfree().

This fix is only necessary with the SLAB allocator and CONFIG_DEBUG_SLAB
enabled;  non-debug SLAB, SLUB do return nicely aligned addresses,
debug-enabled SLUB currently panics early in the boot process.

Signed-off-by: Manuel Lauss <>
v2: slightly improved the patch rationale, thanks to David Daney.

 arch/mips/alchemy/common/dbdma.c                 |    7 +++++--
 arch/mips/include/asm/mach-au1x00/au1xxx_dbdma.h |    1 +
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/mips/alchemy/common/dbdma.c b/arch/mips/alchemy/common/dbdma.c
index 40071bd..3b2ccc0 100644
--- a/arch/mips/alchemy/common/dbdma.c
+++ b/arch/mips/alchemy/common/dbdma.c
@@ -411,8 +411,11 @@ u32 au1xxx_dbdma_ring_alloc(u32 chanid, int entries)
                if (desc_base == 0)
                        return 0;
+               ctp->cdb_membase = desc_base;
                desc_base = ALIGN_ADDR(desc_base, sizeof(au1x_ddma_desc_t));
-       }
+       } else
+               ctp->cdb_membase = desc_base;
        dp = (au1x_ddma_desc_t *)desc_base;
        /* Keep track of the base descriptor. */
@@ -829,7 +832,7 @@ void au1xxx_dbdma_chan_free(u32 chanid)
-       kfree((void *)ctp->chan_desc_base);
+       kfree((void *)ctp->cdb_membase);
        stp->dev_flags &= ~DEV_FLAGS_INUSE;
        dtp->dev_flags &= ~DEV_FLAGS_INUSE;
diff --git a/arch/mips/include/asm/mach-au1x00/au1xxx_dbdma.h 
index c098b45..8c6b110 100644
--- a/arch/mips/include/asm/mach-au1x00/au1xxx_dbdma.h
+++ b/arch/mips/include/asm/mach-au1x00/au1xxx_dbdma.h
@@ -305,6 +305,7 @@ typedef struct dbdma_chan_config {
        dbdev_tab_t             *chan_dest;
        au1x_dma_chan_t         *chan_ptr;
        au1x_ddma_desc_t        *chan_desc_base;
+       u32                     cdb_membase; /* kmalloc base of above */
        au1x_ddma_desc_t        *get_ptr, *put_ptr, *cur_ptr;
        void                    *chan_callparam;
        void                    (*chan_callback)(int, void *);

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