linux-kernel - Re: [patch] swiotlb: fix ignored DMA_ATTR_NO

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Date:   Sat, 12 May 2018 09:11:00 +0200
From:   Mike Galbraith <efault@....de>
To:     nouveau <nouveau@...ts.freedesktop.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Christian Koenig <christian.koenig@....com>,
        Roger He <Hongbo.He@....com>, Christoph Hellwig <hch@....de>
Subject: Re: [patch] swiotlb: fix ignored DMA_ATTR_NO_WARN request

To conclude to this snail like thread (/me=walking wounded), with the
v4.16.8 hunk below, traces showing that swiotlb_alloc_coherent() was
being asked to not bother warning started showing up after the box had
been flogged for a while.

Whatever finally happens with swiotlb (seems to be in flux), other
folks meeting annoying gripeage can find bandaids in the interim.

The End

v4.16.8 !DMA_DIRECT_OPS
Xorg-3105  [001] ....  2156.711471: swiotlb_alloc_coherent+0xa7/0x1e0: yup
Xorg-3105  [001] ....  2156.711497: <stack trace>
 => ttm_dma_populate+0x23c/0x310 [ttm]
 => ttm_tt_bind+0x31/0x60 [ttm]
 => ttm_bo_handle_move_mem+0x527/0x580 [ttm]
 => ttm_bo_validate+0xfb/0x110 [ttm]
 => ttm_bo_init_reserved+0x289/0x450 [ttm]
 => ttm_bo_init+0x77/0xd0 [ttm]
 => nouveau_bo_new+0x3fc/0x5e0 [nouveau]
 => nouveau_gem_new+0x66/0x110 [nouveau]
 => nouveau_gem_ioctl_new+0x48/0xc0 [nouveau]
 => drm_ioctl_kernel+0x66/0xb0 [drm]
 => drm_ioctl+0x2a4/0x360 [drm]
 => nouveau_drm_ioctl+0x50/0xb0 [nouveau]
 => do_vfs_ioctl+0x92/0x5e0
 => SyS_ioctl+0x3b/0x70
 => do_syscall_64+0x74/0x1a0
 => entry_SYSCALL_64_after_hwframe+0x3d/0xa2

--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -28,10 +28,8 @@ void *x86_swiotlb_alloc_coherent(struct
 	 * swiotlb_alloc_coherent() will print a warning when the DMA
 	 * memory allocation ultimately failed.
 	 */
-	flags |= __GFP_NOWARN;
-
-	vaddr = dma_generic_alloc_coherent(hwdev, size, dma_handle, flags,
-					   attrs);
+	vaddr = dma_generic_alloc_coherent(hwdev, size, dma_handle,
+					   flags | __GFP_NOWARN, attrs);
 	if (vaddr)
 		return vaddr;