CVE-2021-47454
- Source
- https://nvd.nist.gov/vuln/detail/CVE-2021-47454
- Import Source
- https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2021-47454.json
- JSON Data
- https://api.test.osv.dev/v1/vulns/CVE-2021-47454
- Related
- Published
- 2024-05-22T07:15:10Z
- Modified
- 2024-09-11T04:41:11.304326Z
- Summary
- [none]
- Details
-
In the Linux kernel, the following vulnerability has been resolved:
powerpc/smp: do not decrement idle task preempt count in CPU offline
With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we get:
BUG: scheduling while atomic: swapper/1/0/0x00000000 no locks held by swapper/1/0. CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100 Call Trace: dumpstacklvl+0xac/0x108 _schedulebug+0xac/0xe0 _schedule+0xcf8/0x10d0 scheduleidle+0x3c/0x70 doidle+0x2d8/0x4a0 cpustartupentry+0x38/0x40 startsecondary+0x2ec/0x3a0 startsecondaryprolog+0x10/0x14
This is because powerpc's archcpuidledead() decrements the idle task's preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc: Re-enable preemption before cpudie()"), specifically "startsecondary() expects a preemptcount() of 0."
However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled"), that justification no longer holds.
The idle task isn't supposed to re-enable preemption, so remove the vestigial preempt_enable() from the CPU offline path.
Tested with pseries and powernv in qemu, and pseries on PowerVM.
- References
Affected packages
Debian:11 / linux
Package
- Name
- linux
- Purl
- pkg:deb/debian/linux?arch=source
Debian:12 / linux
Package
- Name
- linux
- Purl
- pkg:deb/debian/linux?arch=source
Debian:13 / linux
Package
- Name
- linux
- Purl
- pkg:deb/debian/linux?arch=source