Hello Baoquan,
On 19/08/24 11:45, Baoquan He wrote:
On 08/19/24 at 09:45am, Sourabh Jain wrote:
Hello Michael and Boaquan
On 01/08/24 12:21, Sourabh Jain wrote:
Hello Michael,
On 01/08/24 08:04, Michael Ellerman wrote:
Sourabh Jain <sourabhjain@xxxxxxxxxxxxx> writes:
The following errors are observed when kexec is done with SMT=off on
powerpc.
[ 358.458385] Removing IBM Power 842 compression device
[ 374.795734] kexec_core: Starting new kernel
[ 374.795748] kexec: Waking offline cpu 1.
[ 374.875695] crash hp: kexec_trylock() failed, elfcorehdr may
be inaccurate
[ 374.935833] kexec: Waking offline cpu 2.
[ 375.015664] crash hp: kexec_trylock() failed, elfcorehdr may
be inaccurate
snip..
[ 375.515823] kexec: Waking offline cpu 6.
[ 375.635667] crash hp: kexec_trylock() failed, elfcorehdr may
be inaccurate
[ 375.695836] kexec: Waking offline cpu 7.
Are they actually errors though? Do they block the actual kexec from
happening? Or are they just warnings in dmesg?
The kexec kernel boots fine.
This warning appears regardless of whether the kdump kernel is loaded.
However, when the kdump kernel is loaded, we will not be able to update
the kdump image (FDT).
I think this should be fine given that kexec is in progress.
Please let me know your opinion.
Because the fix looks like it could be racy.
It seems like it is racy, but given that kexec takes the lock first and
then
brings the CPU up, which triggers the kdump image, which always fails to
update the kdump image because it could not take the same lock.
Note: the kexec lock is not released unless kexec boot fails.
Any comments or suggestions on this fix?
Is this a little better?
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 63cf89393c6e..0355ffb712f4 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -504,7 +504,7 @@ int crash_check_hotplug_support(void)
crash_hotplug_lock();
/* Obtain lock while reading crash information */
- if (!kexec_trylock()) {
+ if (!kexec_trylock() && kexec_in_progress) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
crash_hotplug_unlock();
return 0;
@@ -539,7 +539,7 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
crash_hotplug_lock();
/* Obtain lock while changing crash information */
- if (!kexec_trylock()) {
+ if (!kexec_trylock() && kexec_in_progress) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
crash_hotplug_unlock();
return;
Ideally, when `kexec_in_progress` is True, there should be no way to
acquire the kexec lock.
Therefore, calling `kexec_trylock()` before checking `kexec_in_progress`
is not helpful.
The kernel will print the error message "kexec_trylock() failed,
elfcorehdr may be inaccurate."
So, with the above changes, the original problem remains unsolved.
However, after closely inspecting the
`kernel/kexec_core.c:kernel_kexec()` function, I discovered
an exceptional case where my patch needs an update. The issue arises
when the system returns
from the `machine_kexec()` function, which indicates that kexec has failed.
In this scenario, the kexec lock is released, but `kexec_in_progress`
remains True.
I am unsure why `kexec_in_progress` is NOT set to False when kexec
fails. Was this by design,
or was it an oversight because returning from the `machine_kexec()`
function is highly unlikely?
Here is my proposal to address the original problem along with the
exceptional case I described
above.
Let's implement two patches:
1. A patch that sets `kexec_in_progress` to False if the system returns
from `machine_kexec()` before
unlocking the kexec lock in the `kernel_kexec()` function.
```
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index c0caa14880c3..b41277183455 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1069,6 +1069,7 @@ int kernel_kexec(void)
#endif
Unlock:
+ kexec_in_progress = false;
kexec_unlock();
return error;
```
2. A patch to return early from the `crash_handle_hotplug_event()`
function if `kexec_in_progress` is
set to True. This is essentially my original patch.
Please share your comments on the new approach.
Thank you for review.
- Sourabh Jain
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