Messages in this thread Patch in this message | | | Subject | Re: [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 | From | Dave Jiang <> | Date | Mon, 6 Jul 2020 08:01:03 -0700 |
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On 7/6/2020 5:53 AM, Arnd Bergmann wrote: > On Mon, Jul 6, 2020 at 1:03 PM Naresh Kamboju <naresh.kamboju@linaro.org> wrote: >> >> While booting qemu_arm64 and qemu_arm with Linux version 5.8.0-rc3-next-20200706 >> the kernel panic noticed due to kernel NULL pointer dereference. >> >> metadata: >> git branch: master >> git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git >> git commit: 5680d14d59bddc8bcbc5badf00dbbd4374858497 >> git describe: next-20200706 >> make_kernelversion: 5.8.0-rc3 >> kernel-config: >> https://builds.tuxbuild.com/Glr-Ql1wbp3qN3cnHogyNA/kernel.config >> >> qemu arm64 boot crash log, >> >> [ 0.972053] Unable to handle kernel NULL pointer dereference at >> virtual address 0000000000000000 >> [ 0.975301] Mem abort info: >> [ 0.976316] ESR = 0x96000004 >> [ 0.977378] EC = 0x25: DABT (current EL), IL = 32 bits >> [ 0.979363] SET = 0, FnV = 0 >> [ 0.980458] EA = 0, S1PTW = 0 >> [ 0.981583] Data abort info: >> [ 0.982634] ISV = 0, ISS = 0x00000004 >> [ 0.984213] CM = 0, WnR = 0 >> [ 0.985260] [0000000000000000] user address but active_mm is swapper >> [ 0.987600] Internal error: Oops: 96000004 [#1] PREEMPT SMP >> [ 0.989557] Modules linked in: >> [ 0.990671] CPU: 2 PID: 1 Comm: swapper/0 Not tainted >> 5.8.0-rc3-next-20200706 #1 >> [ 0.993711] Hardware name: linux,dummy-virt (DT) >> [ 0.995708] pstate: 00000005 (nzcv daif -PAN -UAO BTYPE=--) >> [ 0.998168] pc : pl011_dma_probe+0x90/0x360 > > This is the code from you vmlinux file: > > ffff8000107233e4: b90087e2 str w2, [sp, #132] > ffff8000107233e8: 97fcf14c bl ffff80001065f918 > <dma_request_chan> > ffff8000107233ec: aa0003f4 mov x20, x0 > ffff8000107233f0: b140041f cmn x0, #0x1, lsl #12 > ffff8000107233f4: 54000488 b.hi ffff800010723484 > <pl011_dma_probe+0x11c> // b.pmore > ffff8000107233f8: f9400280 ldr x0, [x20] > ffff8000107233fc: f9409c02 ldr x2, [x0, #312] > ffff800010723400: b4000082 cbz x2, ffff800010723410 > <pl011_dma_probe+0xa8> > > It's the "ldr x0, [x20]" dereferencing 'chan' in pl011_dma_probe() after > checking it for an error value. However it's a NULL pointer, not an > error pointer, indicating that there is a bug in the dmaengine driver > that you use here, or in the dmaengine core code.
Arnd, I'm looking at the pl001_dma_probe(), I think we could make it more robust if it uses IS_ERR_OR_NULL(chan) instead of IS_ERR(). Should I send a patch for it? I suppose looking at the comment header for dma_request_chan() it does say return chan ptr or error ptr. Sorry I missed that.
Vinod, It looks like the only fix for dmaengine for the patch is where Arnd pointed out as far as I can tell after auditing it. Let me know how you want to handle this. Thanks!
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 0d6529eff66f..48e159e83cf5 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -852,7 +852,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name) mutex_lock(&dma_list_mutex); if (list_empty(&dma_device_list)) { mutex_unlock(&dma_list_mutex); - return NULL; + return ERR_PTR(-ENODEV); }
list_for_each_entry_safe(d, _d, &dma_device_list, global_node) {
> > I don't see anything suspicious in dmaengine drivers, but there is a > recent series > from Dave Jiang that might explain it. Could you try reverting commit > deb9541f5052 ("dmaengine: check device and channel list for empty")? > > I think the broken change is this one: > > @@ -819,6 +850,11 @@ struct dma_chan *dma_request_chan(struct device > *dev, const char *name) > > /* Try to find the channel via the DMA filter map(s) */ > mutex_lock(&dma_list_mutex); > + if (list_empty(&dma_device_list)) { > + mutex_unlock(&dma_list_mutex); > + return NULL; > + } > + > list_for_each_entry_safe(d, _d, &dma_device_list, global_node) { > dma_cap_mask_t mask; > const struct dma_slave_map *map = dma_filter_match(d, > name, dev); > > which needs to return an error code like -ENODEV instead of NULL. There > may be other changes in the same patch that introduce the same bug > elsewhere. > > Arnd >
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