linux-kernel - [PATCH] dma-mapping: Remove WARN_ON in dma_free

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Date:	Mon, 29 Mar 2010 20:09:21 +0200
From:	Stefan Bader <stefan.bader@...onical.com>
To:	hpa@...or.com
Cc:	linux-kernel@...r.kernel.org, James.Bottomley@...e.de,
	matthew@....cx
Subject: [PATCH] dma-mapping: Remove WARN_ON in dma_free_coherent

BugLink: http://bugs.launchpad.net/ubuntu/bugs/458201

Triggered by the following backtrace I was looking at the sym53c8xx_2
driver and in there whether it would be possible to avoid the WARN_ON.

WARNING: at
/build/buildd/linux-2.6.32/arch/x86/include/asm/dma-mapping.h:154
___free_dma_mem_cluster+0x102/0x110()

 [<ffffffff81064f9b>] warn_slowpath_common+0x7b/0xc0
 [<ffffffff81064ff4>] warn_slowpath_null+0x14/0x20
 [<ffffffff8139a2a2>] ___free_dma_mem_cluster+0x102/0x110
 [<ffffffff8139a072>] __sym_mfree+0xd2/0x100
 [<ffffffff8139a109>] __sym_mfree_dma+0x69/0x100
 [<ffffffff8139245f>] sym_hcb_free+0x8f/0x1f0

But it seems modifying that driver would be a bigger effort and maybe
not really worthwile as it is a rather old driver. On the other side
I was told [1] that this WARN_ON applies only to ARM which could sleep
in the free path and it is just bogus for X86. As the code is in
arch/x86 it would never be used for anything else than X86 and if
its truely bogus on X86, couldn't it get removed?

[1] http://kerneltrap.org/mailarchive/linux-scsi/2010/3/25/6886023

Signed-off-by: Stefan Bader <stefan.bader@...onical.com>
---
 arch/x86/include/asm/dma-mapping.h |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
index 6a25d5d..2d6097f 100644
--- a/arch/x86/include/asm/dma-mapping.h
+++ b/arch/x86/include/asm/dma-mapping.h
@@ -151,8 +151,6 @@ static inline void dma_free_coherent(struct device *dev, size_t size,
 {
 	struct dma_map_ops *ops = get_dma_ops(dev);
 
-	WARN_ON(irqs_disabled());       /* for portability */
-
 	if (dma_release_from_coherent(dev, get_order(size), vaddr))
 		return;
 
-- 
1.6.3.3

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