Hi Guenter, >> The first time around I was 0/ changing fonts 1/ trimming the dump message >> in the kernel 2/ filming my screen. That's not practical at all... Mmm, pstore does seem to work on my machine. CHROME_PSTORE is not available to me because I'm not on x86, I just enabled the rest and nothing pops up in /sys/fs/pstore... So I took pictures (OCR did not help): - https://funyu.konbu.org/pQUF2P08etcpVxuKZ0A720%2b0/IMG_20200215_134343.jpg.webp is a stack trace for your earlier patch "min_t", in https://www.spinics.net/lists/linux-usb/msg191019.html ; - https://funyu.konbu.org/pQUF2P08etcpVxuKZ0A720%2b0/IMG_20200215_135816.jpg.webp is a stack trace for your later patch "container_of", in https://www.spinics.net/lists/linux-usb/msg191074.html . Both patches crash (without even loading the machine), but "container_of" is a bit more resilient. Thanks, Boris. Guenter Roeck wrote: >Hi Boris, > >On Tue, Feb 11, 2020 at 02:49:53PM +0900, Boris ARZUR wrote: >> Hello Guenter, >> >> >In the meantime, can you by any chance test the attached patch ? It _might_ >> >fix the problem, but it is a bit of a wild shot. >> I tried your patch, but the machine does not finish booting. >> >> >> I would like to give you a dump, but the screen scrolls fast, and what's >> left when paused is not interesting. How do I get it to dump on disk? >> >> My journalctl doesn't show anything. I have no kmesg.log anywhere. >> The first time around I was 0/ changing fonts 1/ trimming the dump message >> in the kernel 2/ filming my screen. That's not practical at all... >> >> >> I have been looking a bit at things. I believe that part of the issue >> is the need to re-align the buffer we get in the URB. I'm wondering if asking >> for a specific alignment when creating the URB could be doable. >> >> >> As a stop-gap, maybe doing things like in tegra ehci could fix our bug: >> https://github.com/torvalds/linux/blob/master/drivers/usb/host/ehci-tegra.c#L288 >> i.e. having the old pointer before the new buffer instead of at the end of >> it. >> >> Now if something is overwriting the buffer end, that would also be hiding the >> issue... but if the bug is related to lengths that don't match between >> allocation and free, that could work. In this case, that would also be >> hiding the issue :) >> >See below for a patch (untested) doing just that. It may solve your immediate >problem, though it would still suffer from the buffer end overwrite. > >> >> >Unfortunately, I have been unable to reproduce the problem. It is seen only >> >with certain phones and with certain Ethernet adapters, and I was unable >> >to get any of those. I'll keep trying. >> If you want, I can run a kernel with some printk instrumentation or run >> experiments. I'll research a bit on how to get that kernel oops data, that > >Unfortunately I have no real idea what to look out for. The problem may be >related to the phone sending more than one Ethernet packet in a single USB >transfer. See rndis_rx_fixup() for how that is handled in the driver. >I don't know how that would result in the observed problem, though. > >Thanks, >Guenter > >--- >From 8efa9c598f2390dca2e97cbbe41e981caba41ca1 Mon Sep 17 00:00:00 2001 >From: Guenter Roeck <linux@xxxxxxxxxxxx> >Date: Mon, 10 Feb 2020 14:04:06 -0800 >Subject: [PATCH] usb: dwc2: Simplify DMA alignment code > >The code to align buffers for DMA was first introduced with commit >3bc04e28a030 ("usb: dwc2: host: Get aligned DMA in a more supported way"). >It was updated with commit 56406e017a88 ("usb: dwc2: Fix DMA alignment >to start at allocated boundary") because it did not really align buffers to >DMA boundaries but to DWC2_USB_DMA_ALIGN. This was then optimized in commit >1e111e885238 ("usb: dwc2: Fix inefficient copy of unaligned buffers") >to only copy actual data rather than the whole buffer. Commit 4a4863bf2e79 >("usb: dwc2: Fix DMA cache alignment issues") changed this further to add >a padding at the end of the buffer to ensure that the old data pointer is >not in the same cache line as the buffer. > >This last commit states "Otherwise, the stored_xfer_buffer gets corrupted >for IN URBs on non-cache-coherent systems". However, such corruptions are >still observed. Either case, DMA is not expected to overwrite more memory >than it is supposed to do, suggesting that the commit may have been hiding >a problem rather than fixing it. > >On top of that, DMA alignment is still not guaranteed since it only happens >if the original buffer is not aligned to DWC2_USB_DMA_ALIGN, which is still >a constant of 4 and not associated with DMA alignment. > >Move the old data pointer back to the beginning of the new buffer, >restoring most of the original commit and to simplify the code. Define >DWC2_USB_DMA_ALIGN to dma_get_cache_alignment() to fix the DMA alignment >for real this time. > >Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> >--- > drivers/usb/dwc2/hcd.c | 50 +++++++++++++++++++----------------------- > 1 file changed, 22 insertions(+), 28 deletions(-) > >diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c >index 2c81b346b464..9e04b3a314eb 100644 >--- a/drivers/usb/dwc2/hcd.c >+++ b/drivers/usb/dwc2/hcd.c >@@ -2470,21 +2470,24 @@ static int dwc2_alloc_split_dma_aligned_buf(struct dwc2_hsotg *hsotg, > return 0; > } > >-#define DWC2_USB_DMA_ALIGN 4 >+#define DWC2_USB_DMA_ALIGN dma_get_cache_alignment() >+ >+struct dma_aligned_buffer { >+ void *kmalloc_ptr; >+ void *old_xfer_buffer; >+ u8 data[0]; >+}; > > static void dwc2_free_dma_aligned_buffer(struct urb *urb) > { >- void *stored_xfer_buffer; >+ struct dma_aligned_buffer *temp; > size_t length; > > if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER)) > return; > >- /* Restore urb->transfer_buffer from the end of the allocated area */ >- memcpy(&stored_xfer_buffer, >- PTR_ALIGN(urb->transfer_buffer + urb->transfer_buffer_length, >- dma_get_cache_alignment()), >- sizeof(urb->transfer_buffer)); >+ temp = container_of(urb->transfer_buffer, >+ struct dma_aligned_buffer, data); > > if (usb_urb_dir_in(urb)) { > if (usb_pipeisoc(urb->pipe)) >@@ -2492,17 +2495,17 @@ static void dwc2_free_dma_aligned_buffer(struct urb *urb) > else > length = urb->actual_length; > >- memcpy(stored_xfer_buffer, urb->transfer_buffer, length); >+ memcpy(temp->old_xfer_buffer, temp->data, length); > } >- kfree(urb->transfer_buffer); >- urb->transfer_buffer = stored_xfer_buffer; >+ urb->transfer_buffer = temp->old_xfer_buffer; >+ kfree(temp->kmalloc_ptr); > > urb->transfer_flags &= ~URB_ALIGNED_TEMP_BUFFER; > } > > static int dwc2_alloc_dma_aligned_buffer(struct urb *urb, gfp_t mem_flags) > { >- void *kmalloc_ptr; >+ struct dma_aligned_buffer *temp, *kmalloc_ptr; > size_t kmalloc_size; > > if (urb->num_sgs || urb->sg || >@@ -2510,31 +2513,22 @@ static int dwc2_alloc_dma_aligned_buffer(struct urb *urb, gfp_t mem_flags) > !((uintptr_t)urb->transfer_buffer & (DWC2_USB_DMA_ALIGN - 1))) > return 0; > >- /* >- * Allocate a buffer with enough padding for original transfer_buffer >- * pointer. This allocation is guaranteed to be aligned properly for >- * DMA >- */ >+ /* Allocate a buffer with enough padding for alignment */ > kmalloc_size = urb->transfer_buffer_length + >- (dma_get_cache_alignment() - 1) + >- sizeof(urb->transfer_buffer); >+ sizeof(struct dma_aligned_buffer) + DWC2_USB_DMA_ALIGN - 1; > > kmalloc_ptr = kmalloc(kmalloc_size, mem_flags); > if (!kmalloc_ptr) > return -ENOMEM; > >- /* >- * Position value of original urb->transfer_buffer pointer to the end >- * of allocation for later referencing >- */ >- memcpy(PTR_ALIGN(kmalloc_ptr + urb->transfer_buffer_length, >- dma_get_cache_alignment()), >- &urb->transfer_buffer, sizeof(urb->transfer_buffer)); >- >+ /* Position our struct dma_aligned_buffer such that data is aligned */ >+ temp = PTR_ALIGN(kmalloc_ptr + 1, DWC2_USB_DMA_ALIGN) - 1; >+ temp->kmalloc_ptr = kmalloc_ptr; >+ temp->old_xfer_buffer = urb->transfer_buffer; > if (usb_urb_dir_out(urb)) >- memcpy(kmalloc_ptr, urb->transfer_buffer, >+ memcpy(temp->data, urb->transfer_buffer, > urb->transfer_buffer_length); >- urb->transfer_buffer = kmalloc_ptr; >+ urb->transfer_buffer = temp->data; > > urb->transfer_flags |= URB_ALIGNED_TEMP_BUFFER; > >-- >2.17.1 >
