On Mon, Jul 6, 2020 at 1:03 PM Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> 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. 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
