| Message ID | s5h36wf6159.wl-tiwai@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, Takashi: we tested for the whole weekend, your patch works, no panic issue seen. You can safe merge you patch. -----Original Message----- From: Takashi Iwai <tiwai@suse.de> Sent: Thursday, July 19, 2018 5:11 PM To: Zhang, Jun <jun.zhang@intel.com> Cc: He, Bo <bo.he@intel.com>; alsa-devel@alsa-project.org; perex@perex.cz; linux-kernel@vger.kernel.org; Zhang, Yanmin <yanmin.zhang@intel.com> Subject: Re: [PATCH] ALSA: core: fix unsigned int pages overflow when comapred On Thu, 19 Jul 2018 08:42:14 +0200, Takashi Iwai wrote: > > On Thu, 19 Jul 2018 08:08:06 +0200, > Zhang, Jun wrote: > > > > Hello, Takashi > > > > I think use our patch, it's NOT possible that the returned size is over sgbuf->tblsize. > > > > In function snd_malloc_sgbuf_pages, > > > > Pages is align page, > > sgbuf->tblsize is align 32*page, > > chunk is align 2^n*page, > > > > in our panic case, pages = 123, tlbsize = 128, 1st loop trunk = 32 > > 2nd loop trunk = 32 3rd loop trunk = 32 4th loop trunk = 16 5th loop > > trunk = 16 So in 5th loop pages-trunk = -5, which make dead loop. > > Looking at the code again, yeah, you are right, that won't happen. > > And now it becomes clear: the fundamental problem is that > snd_dma_alloc_pages_fallback() returns a larger size than requested. > It would be acceptable if the internal allocator aligns a larger size, > but it shouldn't appear in the returned size outside. I believe this > was just a misunderstanding of get_order() usage there. > (BTW, it's interesting that the allocation with a larger block worked > while allocation with a smaller chunk failed; it must be a rare case > and that's one of reasons this bug didn't hit frequently.) > > That being said, what we should fix is rather the function > snd_dma_alloc_pages_fallback() to behave as expected, and it'll be > like the patch below. And we can reduce even more lines. A proper patch is below. thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@suse.de> Subject: [PATCH] ALSA: memalloc: Don't exceed over the requested size snd_dma_alloc_pages_fallback() tries to allocate pages again when the allocation fails with reduced size. But the first try actually *increases* the size to power-of-two, which may give back a larger chunk than the requested size. This confuses the callers, e.g. sgbuf assumes that the size is equal or less, and it may result in a bad loop due to the underflow and eventually lead to Oops. The code of this function seems incorrectly assuming the usage of get_order(). We need to decrease at first, then align to power-of-two. Reported-by: he, bo <bo.he@intel.com> Reported-by: zhang jun <jun.zhang@intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de> --- sound/core/memalloc.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c index 7f89d3c79a4b..753d5fc4b284 100644 --- a/sound/core/memalloc.c +++ b/sound/core/memalloc.c @@ -242,16 +242,12 @@ int snd_dma_alloc_pages_fallback(int type, struct device *device, size_t size, int err; while ((err = snd_dma_alloc_pages(type, device, size, dmab)) < 0) { - size_t aligned_size; if (err != -ENOMEM) return err; if (size <= PAGE_SIZE) return -ENOMEM; - aligned_size = PAGE_SIZE << get_order(size); - if (size != aligned_size) - size = aligned_size; - else - size >>= 1; + size >>= 1; + size = PAGE_SIZE << get_order(size); } if (! dmab->area) return -ENOMEM; -- 2.18.0
On Mon, 23 Jul 2018 02:47:18 +0200, He, Bo wrote: > > Hi, Takashi: > we tested for the whole weekend, your patch works, no panic issue seen. You can safe merge you patch. OK, thanks for testing! Now it's merged. Takashi > > -----Original Message----- > From: Takashi Iwai <tiwai@suse.de> > Sent: Thursday, July 19, 2018 5:11 PM > To: Zhang, Jun <jun.zhang@intel.com> > Cc: He, Bo <bo.he@intel.com>; alsa-devel@alsa-project.org; perex@perex.cz; linux-kernel@vger.kernel.org; Zhang, Yanmin <yanmin.zhang@intel.com> > Subject: Re: [PATCH] ALSA: core: fix unsigned int pages overflow when comapred > > On Thu, 19 Jul 2018 08:42:14 +0200, > Takashi Iwai wrote: > > > > On Thu, 19 Jul 2018 08:08:06 +0200, > > Zhang, Jun wrote: > > > > > > Hello, Takashi > > > > > > I think use our patch, it's NOT possible that the returned size is over sgbuf->tblsize. > > > > > > In function snd_malloc_sgbuf_pages, > > > > > > Pages is align page, > > > sgbuf->tblsize is align 32*page, > > > chunk is align 2^n*page, > > > > > > in our panic case, pages = 123, tlbsize = 128, 1st loop trunk = 32 > > > 2nd loop trunk = 32 3rd loop trunk = 32 4th loop trunk = 16 5th loop > > > trunk = 16 So in 5th loop pages-trunk = -5, which make dead loop. > > > > Looking at the code again, yeah, you are right, that won't happen. > > > > And now it becomes clear: the fundamental problem is that > > snd_dma_alloc_pages_fallback() returns a larger size than requested. > > It would be acceptable if the internal allocator aligns a larger size, > > but it shouldn't appear in the returned size outside. I believe this > > was just a misunderstanding of get_order() usage there. > > (BTW, it's interesting that the allocation with a larger block worked > > while allocation with a smaller chunk failed; it must be a rare case > > and that's one of reasons this bug didn't hit frequently.) > > > > That being said, what we should fix is rather the function > > snd_dma_alloc_pages_fallback() to behave as expected, and it'll be > > like the patch below. > > And we can reduce even more lines. A proper patch is below. > > > thanks, > > Takashi > > -- 8< -- > From: Takashi Iwai <tiwai@suse.de> > Subject: [PATCH] ALSA: memalloc: Don't exceed over the requested size > > snd_dma_alloc_pages_fallback() tries to allocate pages again when the allocation fails with reduced size. But the first try actually > *increases* the size to power-of-two, which may give back a larger chunk than the requested size. This confuses the callers, e.g. sgbuf assumes that the size is equal or less, and it may result in a bad loop due to the underflow and eventually lead to Oops. > > The code of this function seems incorrectly assuming the usage of get_order(). We need to decrease at first, then align to power-of-two. > > Reported-by: he, bo <bo.he@intel.com> > Reported-by: zhang jun <jun.zhang@intel.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Takashi Iwai <tiwai@suse.de> > --- > sound/core/memalloc.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c index 7f89d3c79a4b..753d5fc4b284 100644 > --- a/sound/core/memalloc.c > +++ b/sound/core/memalloc.c > @@ -242,16 +242,12 @@ int snd_dma_alloc_pages_fallback(int type, struct device *device, size_t size, > int err; > > while ((err = snd_dma_alloc_pages(type, device, size, dmab)) < 0) { > - size_t aligned_size; > if (err != -ENOMEM) > return err; > if (size <= PAGE_SIZE) > return -ENOMEM; > - aligned_size = PAGE_SIZE << get_order(size); > - if (size != aligned_size) > - size = aligned_size; > - else > - size >>= 1; > + size >>= 1; > + size = PAGE_SIZE << get_order(size); > } > if (! dmab->area) > return -ENOMEM; > -- > 2.18.0 >
diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c index 7f89d3c79a4b..753d5fc4b284 100644 --- a/sound/core/memalloc.c +++ b/sound/core/memalloc.c @@ -242,16 +242,12 @@ int snd_dma_alloc_pages_fallback(int type, struct device *device, size_t size, int err; while ((err = snd_dma_alloc_pages(type, device, size, dmab)) < 0) { - size_t aligned_size; if (err != -ENOMEM) return err; if (size <= PAGE_SIZE) return -ENOMEM; - aligned_size = PAGE_SIZE << get_order(size); - if (size != aligned_size) - size = aligned_size; - else - size >>= 1; + size >>= 1; + size = PAGE_SIZE << get_order(size); } if (! dmab->area) return -ENOMEM;