{"id":"CVE-2021-46939","state":"PUBLISHED","title":"tracing: Restructure trace_clock_global() to never block","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Restructure trace_clock_global() to never block\n\nIt was reported that a fix to the ring buffer recursion detection would\ncause a hung machine when performing suspend / resume testing. The\nfollowing backtrace was extracted from debugging that case:\n\nCall Trace:\n trace_clock_global+0x91/0xa0\n __rb_reserve_next+0x237/0x460\n ring_buffer_lock_reserve+0x12a/0x3f0\n trace_buffer_lock_reserve+0x10/0x50\n __trace_graph_return+0x1f/0x80\n trace_graph_return+0xb7/0xf0\n ? trace_clock_global+0x91/0xa0\n ftrace_return_to_handler+0x8b/0xf0\n ? pv_hash+0xa0/0xa0\n return_to_handler+0x15/0x30\n ? ftrace_graph_caller+0xa0/0xa0\n ? trace_clock_global+0x91/0xa0\n ? __rb_reserve_next+0x237/0x460\n ? ring_buffer_lock_reserve+0x12a/0x3f0\n ? trace_event_buffer_lock_reserve+0x3c/0x120\n ? trace_event_buffer_reserve+0x6b/0xc0\n ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0\n ? dpm_run_callback+0x3b/0xc0\n ? pm_ops_is_empty+0x50/0x50\n ? platform_get_irq_byname_optional+0x90/0x90\n ? trace_device_pm_callback_start+0x82/0xd0\n ? dpm_run_callback+0x49/0xc0\n\nWith the following RIP:\n\nRIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200\n\nSince the fix to the recursion detection would allow a single recursion to\nhappen while tracing, this lead to the trace_clock_global() taking a spin\nlock and then trying to take it again:\n\nring_buffer_lock_reserve() {\n  trace_clock_global() {\n    arch_spin_lock() {\n      queued_spin_lock_slowpath() {\n        /* lock taken */\n        (something else gets traced by function graph tracer)\n          ring_buffer_lock_reserve() {\n            trace_clock_global() {\n              arch_spin_lock() {\n                queued_spin_lock_slowpath() {\n                /* DEAD LOCK! */\n\nTracing should *never* block, as it can lead to strange lockups like the\nabove.\n\nRestructure the trace_clock_global() code to instead of simply taking a\nlock to update the recorded \"prev_time\" simply use it, as two events\nhappening on two different CPUs that calls this at the same time, really\ndoesn't matter which one goes first. Use a trylock to grab the lock for\nupdating the prev_time, and if it fails, simply try again the next time.\nIf it failed to be taken, that means something else is already updating\nit.\n\n\nBugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761","publishedAt":"2024-02-27T18:40:27.471Z","updatedAt":"2026-05-11T13:44:49.866Z","severity":{"score":5.5,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","source":"CISA-ADP"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"91ca6f6a91f679c8645d7f3307e03ce86ad518c4","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"1fca00920327be96f3318224f502e4d5460f9545","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"d43d56dbf452ccecc1ec735cd4b6840118005d7c","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"c64da3294a7d59a4bf6874c664c13be892f15f44","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"a33614d52e97fc8077eb0b292189ca7d964cc534","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"6e2418576228eeb12e7ba82edb8f9500623942ff","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"2a1bd74b8186d7938bf004f5603f25b84785f63e","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"aafe104aa9096827a429bc1358f8260ee565b7cc","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/trace/trace_clock.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.30","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.30","versionType":"semver"},{"version":"4.4.269","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.269","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.233","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.191","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.118","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.36","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.11.20","status":"unaffected","lessThanOrEqual":"5.11.*","versionType":"semver"},{"version":"5.12.3","status":"unaffected","lessThanOrEqual":"5.12.*","versionType":"semver"},{"version":"5.13","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/trace/trace_clock.c"]}],"references":["https://git.kernel.org/stable/c/91ca6f6a91f679c8645d7f3307e03ce86ad518c4","https://git.kernel.org/stable/c/859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b","https://git.kernel.org/stable/c/1fca00920327be96f3318224f502e4d5460f9545","https://git.kernel.org/stable/c/d43d56dbf452ccecc1ec735cd4b6840118005d7c","https://git.kernel.org/stable/c/c64da3294a7d59a4bf6874c664c13be892f15f44","https://git.kernel.org/stable/c/a33614d52e97fc8077eb0b292189ca7d964cc534","https://git.kernel.org/stable/c/6e2418576228eeb12e7ba82edb8f9500623942ff","https://git.kernel.org/stable/c/2a1bd74b8186d7938bf004f5603f25b84785f63e","https://git.kernel.org/stable/c/aafe104aa9096827a429bc1358f8260ee565b7cc"],"weaknesses":["CWE-400"],"ingestedAt":"2026-10-29T19:49:16.371Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/46xxx/CVE-2021-46939.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-46939","state":"PUBLISHED","datePublished":"2024-02-27T18:40:27.471Z","dateUpdated":"2026-05-11T13:44:49.866Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-02-25T13:45:52.721Z"},"containers":{"cna":{"title":"tracing: Restructure trace_clock_global() to never block","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Restructure trace_clock_global() to never block\n\nIt was reported that a fix to the ring buffer recursion detection would\ncause a hung machine when performing suspend / resume testing. The\nfollowing backtrace was extracted from debugging that case:\n\nCall Trace:\n trace_clock_global+0x91/0xa0\n __rb_reserve_next+0x237/0x460\n ring_buffer_lock_reserve+0x12a/0x3f0\n trace_buffer_lock_reserve+0x10/0x50\n __trace_graph_return+0x1f/0x80\n trace_graph_return+0xb7/0xf0\n ? trace_clock_global+0x91/0xa0\n ftrace_return_to_handler+0x8b/0xf0\n ? pv_hash+0xa0/0xa0\n return_to_handler+0x15/0x30\n ? ftrace_graph_caller+0xa0/0xa0\n ? trace_clock_global+0x91/0xa0\n ? __rb_reserve_next+0x237/0x460\n ? ring_buffer_lock_reserve+0x12a/0x3f0\n ? trace_event_buffer_lock_reserve+0x3c/0x120\n ? trace_event_buffer_reserve+0x6b/0xc0\n ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0\n ? dpm_run_callback+0x3b/0xc0\n ? pm_ops_is_empty+0x50/0x50\n ? platform_get_irq_byname_optional+0x90/0x90\n ? trace_device_pm_callback_start+0x82/0xd0\n ? dpm_run_callback+0x49/0xc0\n\nWith the following RIP:\n\nRIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200\n\nSince the fix to the recursion detection would allow a single recursion to\nhappen while tracing, this lead to the trace_clock_global() taking a spin\nlock and then trying to take it again:\n\nring_buffer_lock_reserve() {\n  trace_clock_global() {\n    arch_spin_lock() {\n      queued_spin_lock_slowpath() {\n        /* lock taken */\n        (something else gets traced by function graph tracer)\n          ring_buffer_lock_reserve() {\n            trace_clock_global() {\n              arch_spin_lock() {\n                queued_spin_lock_slowpath() {\n                /* DEAD LOCK! */\n\nTracing should *never* block, as it can lead to strange lockups like the\nabove.\n\nRestructure the trace_clock_global() code to instead of simply taking a\nlock to update the recorded \"prev_time\" simply use it, as two events\nhappening on two different CPUs that calls this at the same time, really\ndoesn't matter which one goes first. Use a trylock to grab the lock for\nupdating the prev_time, and if it fails, simply try again the next time.\nIf it failed to be taken, that means something else is already updating\nit.\n\n\nBugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"91ca6f6a91f679c8645d7f3307e03ce86ad518c4","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"1fca00920327be96f3318224f502e4d5460f9545","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"d43d56dbf452ccecc1ec735cd4b6840118005d7c","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"c64da3294a7d59a4bf6874c664c13be892f15f44","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"a33614d52e97fc8077eb0b292189ca7d964cc534","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"6e2418576228eeb12e7ba82edb8f9500623942ff","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"2a1bd74b8186d7938bf004f5603f25b84785f63e","versionType":"git"},{"version":"14131f2f98ac350ee9e73faed916d2238a8b6a0d","status":"affected","lessThan":"aafe104aa9096827a429bc1358f8260ee565b7cc","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/trace/trace_clock.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.30","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.30","versionType":"semver"},{"version":"4.4.269","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.269","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.233","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.191","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.118","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.36","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.11.20","status":"unaffected","lessThanOrEqual":"5.11.*","versionType":"semver"},{"version":"5.12.3","status":"unaffected","lessThanOrEqual":"5.12.*","versionType":"semver"},{"version":"5.13","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/trace/trace_clock.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/91ca6f6a91f679c8645d7f3307e03ce86ad518c4"},{"url":"https://git.kernel.org/stable/c/859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b"},{"url":"https://git.kernel.org/stable/c/1fca00920327be96f3318224f502e4d5460f9545"},{"url":"https://git.kernel.org/stable/c/d43d56dbf452ccecc1ec735cd4b6840118005d7c"},{"url":"https://git.kernel.org/stable/c/c64da3294a7d59a4bf6874c664c13be892f15f44"},{"url":"https://git.kernel.org/stable/c/a33614d52e97fc8077eb0b292189ca7d964cc534"},{"url":"https://git.kernel.org/stable/c/6e2418576228eeb12e7ba82edb8f9500623942ff"},{"url":"https://git.kernel.org/stable/c/2a1bd74b8186d7938bf004f5603f25b84785f63e"},{"url":"https://git.kernel.org/stable/c/aafe104aa9096827a429bc1358f8260ee565b7cc"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T13:44:49.866Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"4.4.269"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"4.9.269"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"4.14.233"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"4.19.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"5.4.118"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"5.10.36"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"5.11.20"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"5.12.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.30","versionEndExcluding":"5.13"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":5.5,"attackVector":"LOCAL","baseSeverity":"MEDIUM","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","integrityImpact":"NONE","userInteraction":"NONE","attackComplexity":"LOW","availabilityImpact":"HIGH","privilegesRequired":"LOW","confidentialityImpact":"NONE"}},{"other":{"type":"ssvc","content":{"timestamp":"2025-04-22T16:06:58.628047Z","id":"CVE-2021-46939","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-400","type":"CWE","lang":"en","description":"CWE-400 Uncontrolled Resource Consumption"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2025-04-22T16:08:05.513Z"}},{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/91ca6f6a91f679c8645d7f3307e03ce86ad518c4","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/1fca00920327be96f3318224f502e4d5460f9545","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/d43d56dbf452ccecc1ec735cd4b6840118005d7c","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/c64da3294a7d59a4bf6874c664c13be892f15f44","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/a33614d52e97fc8077eb0b292189ca7d964cc534","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/6e2418576228eeb12e7ba82edb8f9500623942ff","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/2a1bd74b8186d7938bf004f5603f25b84785f63e","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/aafe104aa9096827a429bc1358f8260ee565b7cc","tags":["x_transferred"]}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2024-08-04T05:17:43.036Z"}}]}}}