| Message ID | alpine.LRH.2.02.1409161236550.3150@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Mikulas, On Tue, Sep 16, 2014 at 6:38 PM, Mikulas Patocka <mpatocka@redhat.com> wrote: > The patch also removes the references to fb_memmove in the code that is > commented out because fb_memmove was removed from framebuffer subsystem. I'd leave it as-is. Using plain memmove() is not correct, as it should operate on MMIO space, not RAM. On x86 it works with memmove(), though, but not on all architectures. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 17 Sep 2014, Geert Uytterhoeven wrote: > Hi Mikulas, > > On Tue, Sep 16, 2014 at 6:38 PM, Mikulas Patocka <mpatocka@redhat.com> wrote: > > The patch also removes the references to fb_memmove in the code that is > > commented out because fb_memmove was removed from framebuffer subsystem. > > I'd leave it as-is. Using plain memmove() is not correct, as it should operate > on MMIO space, not RAM. On x86 it works with memmove(), though, but > not on all architectures. > > Gr{oetje,eeting}s, > > Geert That code is disabled with #if 0. So it doesn't matter if it's incorrect in some specific situation. The purpose of that disabled code is to be able to verify that the bug is in bitcpy_rev. I get screen corruption - so I enable that "memmove" statement - the screen corruption goes away - so I know that the bug is in bitcpy_rev. Mikulas -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 16/09/14 19:38, Mikulas Patocka wrote: > The function bitcpy_rev has a bug that may result in screen corruption. > The bug happens under these conditions: > * the end of the destination area of a copy operation is aligned on a long > word boundary > * the end of the source area is not aligned on a long word boundary > * we are copying more than one long word > > In this case, the variable shift is non-zero and the variable first is > zero. The statements FB_WRITEL(comp(d0, FB_READL(dst), first), dst) reads > the last long word of the destination and writes it back unchanged > (because first is zero). Correctly, we should write the variable d0 to the > last word of the destination in this case. > > This patch fixes the bug by introducing and extra test if first is zero. > > The patch also removes the references to fb_memmove in the code that is > commented out because fb_memmove was removed from framebuffer subsystem. Thanks, queued for 3.18. Tomi
Index: linux-3.16.1/drivers/video/fbdev/core/cfbcopyarea.c =================================================================== --- linux-3.16.1.orig/drivers/video/cfbcopyarea.c +++ linux-3.16.1/drivers/video/fbdev/core/cfbcopyarea.c @@ -55,8 +55,8 @@ bitcpy(struct fb_info *p, unsigned long * If you suspect bug in this function, compare it with this simple * memmove implementation. */ - fb_memmove((char *)dst + ((dst_idx & (bits - 1))) / 8, - (char *)src + ((src_idx & (bits - 1))) / 8, n / 8); + memmove((char *)dst + ((dst_idx & (bits - 1))) / 8, + (char *)src + ((src_idx & (bits - 1))) / 8, n / 8); return; #endif @@ -221,8 +221,8 @@ bitcpy_rev(struct fb_info *p, unsigned l * If you suspect bug in this function, compare it with this simple * memmove implementation. */ - fb_memmove((char *)dst + ((dst_idx & (bits - 1))) / 8, - (char *)src + ((src_idx & (bits - 1))) / 8, n / 8); + memmove((char *)dst + ((dst_idx & (bits - 1))) / 8, + (char *)src + ((src_idx & (bits - 1))) / 8, n / 8); return; #endif @@ -324,7 +324,10 @@ bitcpy_rev(struct fb_info *p, unsigned l d0 = d0 << left | d1 >> right; } d0 = fb_rev_pixels_in_long(d0, bswapmask); - FB_WRITEL(comp(d0, FB_READL(dst), first), dst); + if (!first) + FB_WRITEL(d0, dst); + else + FB_WRITEL(comp(d0, FB_READL(dst), first), dst); d0 = d1; dst--; n -= dst_idx+1;
The function bitcpy_rev has a bug that may result in screen corruption. The bug happens under these conditions: * the end of the destination area of a copy operation is aligned on a long word boundary * the end of the source area is not aligned on a long word boundary * we are copying more than one long word In this case, the variable shift is non-zero and the variable first is zero. The statements FB_WRITEL(comp(d0, FB_READL(dst), first), dst) reads the last long word of the destination and writes it back unchanged (because first is zero). Correctly, we should write the variable d0 to the last word of the destination in this case. This patch fixes the bug by introducing and extra test if first is zero. The patch also removes the references to fb_memmove in the code that is commented out because fb_memmove was removed from framebuffer subsystem. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: stable@vger.kernel.org -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html