When I combined kgdboc_earlycon with an inflight patch titled ("soc:
qcom-geni-se: Add interconnect support to fix earlycon crash") [1]
things went boom. Specifically I got a crash during the transition
between kgdboc_earlycon and the main kgdboc that looked like this:
Call trace:
__schedule_bug+0x68/0x6c
__schedule+0x75c/0x924
schedule+0x8c/0xbc
schedule_timeout+0x9c/0xfc
do_wait_for_common+0xd0/0x160
wait_for_completion_timeout+0x54/0x74
rpmh_write_batch+0x1fc/0x23c
qcom_icc_bcm_voter_commit+0x1b4/0x388
qcom_icc_set+0x2c/0x3c
apply_constraints+0x5c/0x98
icc_set_bw+0x204/0x3bc
icc_put+0x30/0xf8
geni_remove_earlycon_icc_vote+0x6c/0x9c
qcom_geni_serial_earlycon_exit+0x10/0x1c
kgdboc_earlycon_deinit+0x38/0x58
kgdb_register_io_module+0x11c/0x194
configure_kgdboc+0x108/0x174
kgdboc_probe+0x38/0x60
platform_drv_probe+0x90/0xb0
really_probe+0x130/0x2fc
...
The problem was that we were holding the "kgdb_registration_lock"
while calling into code that didn't expect to be called in spinlock
context.
Let's slightly defer when we call the deinit code so that it's not
done under spinlock.
NOTE: this does mean that the "deinit" call of the old kgdb IO module
is now made _after_ the init of the new IO module, but presumably
that's OK.
[1] https://lkml.kernel.org/r/[email protected]
Fixes: 220995622da5 ("kgdboc: Add kgdboc_earlycon to support early kgdb using boot consoles")
Signed-off-by: Douglas Anderson <[email protected]>
---
kernel/debug/debug_core.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 4d59aa907fdc..ef94e906f05a 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -1089,7 +1089,6 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
}
pr_info("Replacing I/O driver %s with %s\n",
old_dbg_io_ops->name, new_dbg_io_ops->name);
- old_dbg_io_ops->deinit();
}
if (new_dbg_io_ops->init) {
@@ -1104,8 +1103,10 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
spin_unlock(&kgdb_registration_lock);
- if (old_dbg_io_ops)
+ if (old_dbg_io_ops) {
+ old_dbg_io_ops->deinit();
return 0;
+ }
pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
--
2.27.0.rc0.183.gde8f92d652-goog
On Tue, May 26, 2020 at 02:20:06PM -0700, Douglas Anderson wrote:
> When I combined kgdboc_earlycon with an inflight patch titled ("soc:
> qcom-geni-se: Add interconnect support to fix earlycon crash") [1]
> things went boom. Specifically I got a crash during the transition
> between kgdboc_earlycon and the main kgdboc that looked like this:
>
> Call trace:
> <snip>
> ...
>
> The problem was that we were holding the "kgdb_registration_lock"
> while calling into code that didn't expect to be called in spinlock
> context.
>
> Let's slightly defer when we call the deinit code so that it's not
> done under spinlock.
>
> NOTE: this does mean that the "deinit" call of the old kgdb IO module
> is now made _after_ the init of the new IO module, but presumably
> that's OK.
>
> [1] https://lkml.kernel.org/r/[email protected]
>
> Fixes: 220995622da5 ("kgdboc: Add kgdboc_earlycon to support early kgdb using boot consoles")
> Signed-off-by: Douglas Anderson <[email protected]>
Just found this in my inbox... which suggested I forgot to post an
"Applied" last week when I pushed it for linux-next.
Expect the kgdb PR for this cycle shortly!
Daniel.
> ---
>
> kernel/debug/debug_core.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 4d59aa907fdc..ef94e906f05a 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -1089,7 +1089,6 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
> }
> pr_info("Replacing I/O driver %s with %s\n",
> old_dbg_io_ops->name, new_dbg_io_ops->name);
> - old_dbg_io_ops->deinit();
> }
>
> if (new_dbg_io_ops->init) {
> @@ -1104,8 +1103,10 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
>
> spin_unlock(&kgdb_registration_lock);
>
> - if (old_dbg_io_ops)
> + if (old_dbg_io_ops) {
> + old_dbg_io_ops->deinit();
> return 0;
> + }
>
> pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
>
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>