** Changed in: linux-riscv-5.11 (Ubuntu Focal)
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/1940426
Title:
Disable ftrace of sbi functions
Status in linux-riscv package in Ubuntu:
Fix Released
Status in linux-riscv-5.11 package in Ubuntu:
Invalid
Status in linux-riscv-5.11 source package in Focal:
Fix Committed
Status in linux-riscv source package in Hirsute:
Confirmed
Bug description:
[Impact]
* A kernel build can fail to boot with Oops and illegal instruction
as seen at https://bugs.launchpad.net/ubuntu/+source/linux-
riscv-5.11/+bug/1934548 on Unmatched board.
* One cannot frace functions, used in frace setup. On RISC-V these
are sbi calls to firmware from sbi.c which were not excluded for
tracing. Similar functions on other arches are already excluded.
* Previously we have identified one call that was racing and causing
failure to boot and marked it for notrace. But the upstream solution
is to disable all functions in sbi.c which was implemented in v5.12
but did not make it to stable/earlier trees.
* Note that this failure to boot is racy, meaning some lucky builds
of kernel always boot or always fail, as was observed on Unmatched.
[Test Plan]
* Kernel should boot on baremetal Unmatched, Unleashed, and qemu
[Where problems could occur]
* This patch disables profiling and tracing of sbi.c function calls.
Previously it was possible to trace them, somewhat, either
successfully in a racy manner or to cause a kernel panic.
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