{"id":"CVE-2021-47454","state":"PUBLISHED","title":"powerpc/smp: do not decrement idle task preempt count in CPU offline","description":"In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/smp: do not decrement idle task preempt count in CPU offline\n\nWith PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we\nget:\n\nBUG: scheduling while atomic: swapper/1/0/0x00000000\nno locks held by swapper/1/0.\nCPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100\nCall Trace:\n dump_stack_lvl+0xac/0x108\n __schedule_bug+0xac/0xe0\n __schedule+0xcf8/0x10d0\n schedule_idle+0x3c/0x70\n do_idle+0x2d8/0x4a0\n cpu_startup_entry+0x38/0x40\n start_secondary+0x2ec/0x3a0\n start_secondary_prolog+0x10/0x14\n\nThis is because powerpc's arch_cpu_idle_dead() decrements the idle task's\npreempt count, for reasons explained in commit a7c2bb8279d2 (\"powerpc:\nRe-enable preemption before cpu_die()\"), specifically \"start_secondary()\nexpects a preempt_count() of 0.\"\n\nHowever, since commit 2c669ef6979c (\"powerpc/preempt: Don't touch the idle\ntask's preempt_count during hotplug\") and commit f1a0a376ca0c (\"sched/core:\nInitialize the idle task with preemption disabled\"), that justification no\nlonger holds.\n\nThe idle task isn't supposed to re-enable preemption, so remove the\nvestigial preempt_enable() from the CPU offline path.\n\nTested with pseries and powernv in qemu, and pseries on PowerVM.","publishedAt":"2024-05-22T06:19:44.040Z","updatedAt":"2026-05-23T15:20:00.262Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bdf4d33e8342b90386156204e1da0cdfdb4bf146","status":"affected","lessThan":"53770a411559cf7bc0906d1df319cc533d2f4f58","versionType":"git"},{"version":"2c669ef6979c370f98d4b876e54f19613c81e075","status":"affected","lessThan":"3ea0b497a7a2fff6a4b7090310c9f52c91975934","versionType":"git"},{"version":"2c669ef6979c370f98d4b876e54f19613c81e075","status":"affected","lessThan":"787252a10d9422f3058df9a4821f389e5326c440","versionType":"git"},{"version":"2b6148ef2bd6d8ddc76e7873114f7769b6aa25f0","status":"affected","versionType":"git"},{"version":"20a015e948b825afb47855de2efce7cae7c2608f","status":"affected","versionType":"git"},{"version":"5.10.50","status":"affected","lessThan":"5.10.76","versionType":"semver"},{"version":"5.12.17","status":"affected","lessThan":"5.13","versionType":"semver"},{"version":"5.13.2","status":"affected","lessThan":"5.14","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kernel/smp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.14","versionType":"semver"},{"version":"5.10.76","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.14.15","status":"unaffected","lessThanOrEqual":"5.14.*","versionType":"semver"},{"version":"5.15","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kernel/smp.c"]}],"references":["https://git.kernel.org/stable/c/53770a411559cf7bc0906d1df319cc533d2f4f58","https://git.kernel.org/stable/c/3ea0b497a7a2fff6a4b7090310c9f52c91975934","https://git.kernel.org/stable/c/787252a10d9422f3058df9a4821f389e5326c440"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47454.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47454","state":"PUBLISHED","datePublished":"2024-05-22T06:19:44.040Z","dateUpdated":"2026-05-23T15:20:00.262Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-05-21T14:58:30.833Z"},"containers":{"cna":{"title":"powerpc/smp: do not decrement idle task preempt count in CPU offline","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/smp: do not decrement idle task preempt count in CPU offline\n\nWith PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we\nget:\n\nBUG: scheduling while atomic: swapper/1/0/0x00000000\nno locks held by swapper/1/0.\nCPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100\nCall Trace:\n dump_stack_lvl+0xac/0x108\n __schedule_bug+0xac/0xe0\n __schedule+0xcf8/0x10d0\n schedule_idle+0x3c/0x70\n do_idle+0x2d8/0x4a0\n cpu_startup_entry+0x38/0x40\n start_secondary+0x2ec/0x3a0\n start_secondary_prolog+0x10/0x14\n\nThis is because powerpc's arch_cpu_idle_dead() decrements the idle task's\npreempt count, for reasons explained in commit a7c2bb8279d2 (\"powerpc:\nRe-enable preemption before cpu_die()\"), specifically \"start_secondary()\nexpects a preempt_count() of 0.\"\n\nHowever, since commit 2c669ef6979c (\"powerpc/preempt: Don't touch the idle\ntask's preempt_count during hotplug\") and commit f1a0a376ca0c (\"sched/core:\nInitialize the idle task with preemption disabled\"), that justification no\nlonger holds.\n\nThe idle task isn't supposed to re-enable preemption, so remove the\nvestigial preempt_enable() from the CPU offline path.\n\nTested with pseries and powernv in qemu, and pseries on PowerVM."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bdf4d33e8342b90386156204e1da0cdfdb4bf146","status":"affected","lessThan":"53770a411559cf7bc0906d1df319cc533d2f4f58","versionType":"git"},{"version":"2c669ef6979c370f98d4b876e54f19613c81e075","status":"affected","lessThan":"3ea0b497a7a2fff6a4b7090310c9f52c91975934","versionType":"git"},{"version":"2c669ef6979c370f98d4b876e54f19613c81e075","status":"affected","lessThan":"787252a10d9422f3058df9a4821f389e5326c440","versionType":"git"},{"version":"2b6148ef2bd6d8ddc76e7873114f7769b6aa25f0","status":"affected","versionType":"git"},{"version":"20a015e948b825afb47855de2efce7cae7c2608f","status":"affected","versionType":"git"},{"version":"5.10.50","status":"affected","lessThan":"5.10.76","versionType":"semver"},{"version":"5.12.17","status":"affected","lessThan":"5.13","versionType":"semver"},{"version":"5.13.2","status":"affected","lessThan":"5.14","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kernel/smp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.14","versionType":"semver"},{"version":"5.10.76","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.14.15","status":"unaffected","lessThanOrEqual":"5.14.*","versionType":"semver"},{"version":"5.15","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kernel/smp.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/53770a411559cf7bc0906d1df319cc533d2f4f58"},{"url":"https://git.kernel.org/stable/c/3ea0b497a7a2fff6a4b7090310c9f52c91975934"},{"url":"https://git.kernel.org/stable/c/787252a10d9422f3058df9a4821f389e5326c440"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-23T15:20:00.262Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.10.50","versionEndExcluding":"5.10.76"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.14","versionEndExcluding":"5.14.15"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.14","versionEndExcluding":"5.15"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12.17"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA 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