On 7/6/2020 5:53 AM, Arnd Bergmann wrote:
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
Vinod,
Do you want a diff fix or a revision of the patch for the fix?
