{"api_version":"1","generated_at":"2026-08-27T19:42:13+00:00","cve":"CVE-2026-80527","urls":{"html":"https://cve.report/CVE-2026-80527","api":"https://cve.report/api/cve/CVE-2026-80527.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-80527","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-80527"},"summary":{"title":"ceph: fix hanging __ceph_get_caps() with stale mds_wanted","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix hanging __ceph_get_caps() with stale mds_wanted\n\nA reader can hang forever in __ceph_get_caps() when the client no\nlonger holds `FILE_RD`, but local cap state still says that the\ncapability is already wanted (via `mds_wanted`).\n\nOne way to trigger this is through MDS cap revocation.  If another\nclient performs a conflicting operation, the MDS can revoke `FILE_RD`\nfrom the reader; the next read then has to reacquire `FILE_RD`.  If\nthe cap update that should request `FILE_RD` never reaches the MDS\nafter `cap->mds_wanted` was raised, the reader is left holding only\nnon-file caps while local `mds_wanted` still includes the file read\ncaps.\n\nIn that state, try_get_cap_refs() sees `need <= mds_wanted` and\nreturns 0, so __ceph_get_caps() just waits on `i_cap_wq`.  If the cap\nupdate that was supposed to request `FILE_RD never reaches the MDS\nafter `cap->mds_wanted was` raised, no further request is sent and the\nwaiter can sleep indefinitely until unrelated cap traffic happens to\nwake it up.\n\nThe ordering issue is that `cap->mds_wanted` is updated in\n__prep_cap() before the `CEPH_MSG_CLIENT_CAPS message` is actually\nqueued for send.  That makes one field serve two different meanings at\nonce: what this client wants, and what the client believes the MDS\nalready knows it wants.\n\nA proper fix would be to split those states and track whether a cap\nupdate is actually in flight or has been observed by the MDS.\nHowever, simply moving the `cap->mds_wanted assignment` later would\nnot be sufficient: queueing the message in the messenger does not\nguarantee that the MDS processed that specific wanted set, and\nreconnect or message loss can still invalidate that assumption.\nFixing that properly would require a larger rework of the cap state\nmachine.\n\nTo allow simpler backports to stable kernels, this patch implements a\nsimpler workaround:\n\n- stop waiting forever in __ceph_get_caps(); after a bounded wait,\n  fall back to the renew path\n\n- make ceph_renew_caps() issue a synchronous `OPEN` request whenever\n  the inode still does not actually hold the wanted caps, instead of\n  only calling ceph_check_caps()\n\nThe extra issued-vs-wanted check in ceph_renew_caps() is necessary\nbecause the previous test only checked whether the inode still had any\nreal caps at all.  That is not enough after revocation: the client can\nstill hold something like `pLs` and yet be missing `FILE_RD`\ncompletely.  In that case, falling back to ceph_check_caps() is not\nsufficient, because it still trusts `cap->mds_wanted` and may resend\nnothing.  By requiring `(issued & wanted) == wanted` before taking the\nasynchronous path, the code only uses ceph_check_caps() when the\n`wanted caps` are already actually issued.  Otherwise, it sends the\nsynchronous `OPEN` renew.\n\nThis preserves the existing asynchronous fast path when the wanted\ncaps are already issued, avoids changing cap-state semantics, and\nfixes the hang by guaranteeing that a stalled waiter eventually\nretries through a path that does not rely on the stale `mds_wanted`\nstate.\n\n[ idryomov: move CEPH_GET_CAPS_WAIT_TIMEOUT from libceph.h to\n  mds_client.h, formatting ]","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-26 15:17:06","updated_at":"2026-08-27 06:17:32"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.5","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.5","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"baseScore":7.5,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/9e55fe24c548ad3163903eb58bb002d28d32a630","name":"https://git.kernel.org/stable/c/9e55fe24c548ad3163903eb58bb002d28d32a630","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c","name":"https://git.kernel.org/stable/c/a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5e84bc6f67e19fdd192d8b215de728acbfc12572","name":"https://git.kernel.org/stable/c/5e84bc6f67e19fdd192d8b215de728acbfc12572","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/fcce1b3be6d286aa80831e730289f4c062053ae6","name":"https://git.kernel.org/stable/c/fcce1b3be6d286aa80831e730289f4c062053ae6","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6","name":"https://git.kernel.org/stable/c/50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5fedf279a1ea369d39c8b06dd4547cdc576065d0","name":"https://git.kernel.org/stable/c/5fedf279a1ea369d39c8b06dd4547cdc576065d0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/b5661524c5a45085a866864ca9b8ae2513dfd67a","name":"https://git.kernel.org/stable/c/b5661524c5a45085a866864ca9b8ae2513dfd67a","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e05c315b4da0c16ea800ee4b2cb6c617f586d1b5","name":"https://git.kernel.org/stable/c/e05c315b4da0c16ea800ee4b2cb6c617f586d1b5","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-80527","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80527","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c b5661524c5a45085a866864ca9b8ae2513dfd67a git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c 5e84bc6f67e19fdd192d8b215de728acbfc12572 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c 5fedf279a1ea369d39c8b06dd4547cdc576065d0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c e05c315b4da0c16ea800ee4b2cb6c617f586d1b5 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.217 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.184 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.153 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.105 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.46 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.10 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["fs/ceph/caps.c","fs/ceph/file.c","fs/ceph/mds_client.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"b5661524c5a45085a866864ca9b8ae2513dfd67a","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"5e84bc6f67e19fdd192d8b215de728acbfc12572","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"5fedf279a1ea369d39c8b06dd4547cdc576065d0","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"e05c315b4da0c16ea800ee4b2cb6c617f586d1b5","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"fcce1b3be6d286aa80831e730289f4c062053ae6","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"9e55fe24c548ad3163903eb58bb002d28d32a630","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"},{"lessThan":"50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6","status":"affected","version":"0a454bdd501ad1aa30bb72e9581efa338ad6ce5c","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["fs/ceph/caps.c","fs/ceph/file.c","fs/ceph/mds_client.h"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"5.8"},{"lessThan":"5.8","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.266","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.217","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.184","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.153","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.105","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.46","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.10","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.266","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.217","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.184","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.153","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.105","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.46","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.10","versionStartIncluding":"5.8","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"5.8","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix hanging __ceph_get_caps() with stale mds_wanted\n\nA reader can hang forever in __ceph_get_caps() when the client no\nlonger holds `FILE_RD`, but local cap state still says that the\ncapability is already wanted (via `mds_wanted`).\n\nOne way to trigger this is through MDS cap revocation.  If another\nclient performs a conflicting operation, the MDS can revoke `FILE_RD`\nfrom the reader; the next read then has to reacquire `FILE_RD`.  If\nthe cap update that should request `FILE_RD` never reaches the MDS\nafter `cap->mds_wanted` was raised, the reader is left holding only\nnon-file caps while local `mds_wanted` still includes the file read\ncaps.\n\nIn that state, try_get_cap_refs() sees `need <= mds_wanted` and\nreturns 0, so __ceph_get_caps() just waits on `i_cap_wq`.  If the cap\nupdate that was supposed to request `FILE_RD never reaches the MDS\nafter `cap->mds_wanted was` raised, no further request is sent and the\nwaiter can sleep indefinitely until unrelated cap traffic happens to\nwake it up.\n\nThe ordering issue is that `cap->mds_wanted` is updated in\n__prep_cap() before the `CEPH_MSG_CLIENT_CAPS message` is actually\nqueued for send.  That makes one field serve two different meanings at\nonce: what this client wants, and what the client believes the MDS\nalready knows it wants.\n\nA proper fix would be to split those states and track whether a cap\nupdate is actually in flight or has been observed by the MDS.\nHowever, simply moving the `cap->mds_wanted assignment` later would\nnot be sufficient: queueing the message in the messenger does not\nguarantee that the MDS processed that specific wanted set, and\nreconnect or message loss can still invalidate that assumption.\nFixing that properly would require a larger rework of the cap state\nmachine.\n\nTo allow simpler backports to stable kernels, this patch implements a\nsimpler workaround:\n\n- stop waiting forever in __ceph_get_caps(); after a bounded wait,\n  fall back to the renew path\n\n- make ceph_renew_caps() issue a synchronous `OPEN` request whenever\n  the inode still does not actually hold the wanted caps, instead of\n  only calling ceph_check_caps()\n\nThe extra issued-vs-wanted check in ceph_renew_caps() is necessary\nbecause the previous test only checked whether the inode still had any\nreal caps at all.  That is not enough after revocation: the client can\nstill hold something like `pLs` and yet be missing `FILE_RD`\ncompletely.  In that case, falling back to ceph_check_caps() is not\nsufficient, because it still trusts `cap->mds_wanted` and may resend\nnothing.  By requiring `(issued & wanted) == wanted` before taking the\nasynchronous path, the code only uses ceph_check_caps() when the\n`wanted caps` are already actually issued.  Otherwise, it sends the\nsynchronous `OPEN` renew.\n\nThis preserves the existing asynchronous fast path when the wanted\ncaps are already issued, avoids changing cap-state semantics, and\nfixes the hang by guaranteeing that a stalled waiter eventually\nretries through a path that does not rely on the stale `mds_wanted`\nstate.\n\n[ idryomov: move CEPH_GET_CAPS_WAIT_TIMEOUT from libceph.h to\n  mds_client.h, formatting ]"}],"metrics":[{"cvssV3_1":{"baseScore":7.5,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"scenarios":[{"lang":"en","value":"AV:N - On nodes with cephfs mounted (common in Ceph/Rook/Kubernetes), a remote Ceph client can perform conflicting writes so the MDS revokes FILE_RD via CEPH_MSG_CLIENT_CAPS over the network; the victim kernel then hits the stale mds_wanted hang on the next VFS read/mmap/ioctl path into __ceph_get_caps().\nAC:L - The fix commit documents MDS cap revocation from another client as a reliable trigger; an attacker controls both sides by holding a second Ceph client session and driving conflicting I/O and reconnect/message-loss timing, without depending on uncontrollable victim heap layout or rare kernel configs.\nPR:N - Exploitation requires no Linux account, capability, or init-namespace root on the victim host; any remote (or co-tenant) Ceph client with write access to the shared file can induce revocation and the hang while victims only perform normal reads on an already-mounted cephfs export.\nUI:N - No interactive victim action is needed beyond routine automated reads on cephfs-backed workloads; the attacker does not require the victim to mount media, click a link, or perform a one-off administrative step at exploitation time.\nS:U - Impact is confined to threads blocked in __ceph_get_caps() on the same host kernel security domain; it does not cross VM, container, or IOMMU boundaries or grant elevated privileges beyond availability loss on the affected client.\nC:N - This is a capability wait-loop logic error with no out-of-bounds access, use-after-free, or information disclosure; stale mds_wanted only prevents cap reacquisition and does not read or leak kernel or file data to an attacker.\nI:N - The bug does not modify inode data, kernel memory, or capabilities; it causes indefinite sleeping in cap acquisition with no path to arbitrary write, metadata corruption, or code execution.\nA:H - Before the fix, __ceph_get_caps() could wait forever on i_cap_wq when mds_wanted falsely indicated FILE_RD was already requested but not issued, hanging the reader thread (read/write/mmap/getattr) until unrelated cap traffic; repeated exploitation can deny service to cephfs-backed applications."}]}],"providerMetadata":{"dateUpdated":"2026-08-27T05:01:22.018Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/b5661524c5a45085a866864ca9b8ae2513dfd67a"},{"url":"https://git.kernel.org/stable/c/5e84bc6f67e19fdd192d8b215de728acbfc12572"},{"url":"https://git.kernel.org/stable/c/5fedf279a1ea369d39c8b06dd4547cdc576065d0"},{"url":"https://git.kernel.org/stable/c/e05c315b4da0c16ea800ee4b2cb6c617f586d1b5"},{"url":"https://git.kernel.org/stable/c/fcce1b3be6d286aa80831e730289f4c062053ae6"},{"url":"https://git.kernel.org/stable/c/a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c"},{"url":"https://git.kernel.org/stable/c/9e55fe24c548ad3163903eb58bb002d28d32a630"},{"url":"https://git.kernel.org/stable/c/50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6"}],"title":"ceph: fix hanging __ceph_get_caps() with stale mds_wanted","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-80527","datePublished":"2026-08-26T14:37:06.178Z","dateReserved":"2026-08-26T14:34:25.764Z","dateUpdated":"2026-08-27T05:01:22.018Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-26 15:17:06","lastModifiedDate":"2026-08-27 06:17:32","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":3.6}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"80527","Ordinal":"1","Title":"ceph: fix hanging __ceph_get_caps() with stale mds_wanted","CVE":"CVE-2026-80527","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"80527","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix hanging __ceph_get_caps() with stale mds_wanted\n\nA reader can hang forever in __ceph_get_caps() when the client no\nlonger holds `FILE_RD`, but local cap state still says that the\ncapability is already wanted (via `mds_wanted`).\n\nOne way to trigger this is through MDS cap revocation.  If another\nclient performs a conflicting operation, the MDS can revoke `FILE_RD`\nfrom the reader; the next read then has to reacquire `FILE_RD`.  If\nthe cap update that should request `FILE_RD` never reaches the MDS\nafter `cap->mds_wanted` was raised, the reader is left holding only\nnon-file caps while local `mds_wanted` still includes the file read\ncaps.\n\nIn that state, try_get_cap_refs() sees `need <= mds_wanted` and\nreturns 0, so __ceph_get_caps() just waits on `i_cap_wq`.  If the cap\nupdate that was supposed to request `FILE_RD never reaches the MDS\nafter `cap->mds_wanted was` raised, no further request is sent and the\nwaiter can sleep indefinitely until unrelated cap traffic happens to\nwake it up.\n\nThe ordering issue is that `cap->mds_wanted` is updated in\n__prep_cap() before the `CEPH_MSG_CLIENT_CAPS message` is actually\nqueued for send.  That makes one field serve two different meanings at\nonce: what this client wants, and what the client believes the MDS\nalready knows it wants.\n\nA proper fix would be to split those states and track whether a cap\nupdate is actually in flight or has been observed by the MDS.\nHowever, simply moving the `cap->mds_wanted assignment` later would\nnot be sufficient: queueing the message in the messenger does not\nguarantee that the MDS processed that specific wanted set, and\nreconnect or message loss can still invalidate that assumption.\nFixing that properly would require a larger rework of the cap state\nmachine.\n\nTo allow simpler backports to stable kernels, this patch implements a\nsimpler workaround:\n\n- stop waiting forever in __ceph_get_caps(); after a bounded wait,\n  fall back to the renew path\n\n- make ceph_renew_caps() issue a synchronous `OPEN` request whenever\n  the inode still does not actually hold the wanted caps, instead of\n  only calling ceph_check_caps()\n\nThe extra issued-vs-wanted check in ceph_renew_caps() is necessary\nbecause the previous test only checked whether the inode still had any\nreal caps at all.  That is not enough after revocation: the client can\nstill hold something like `pLs` and yet be missing `FILE_RD`\ncompletely.  In that case, falling back to ceph_check_caps() is not\nsufficient, because it still trusts `cap->mds_wanted` and may resend\nnothing.  By requiring `(issued & wanted) == wanted` before taking the\nasynchronous path, the code only uses ceph_check_caps() when the\n`wanted caps` are already actually issued.  Otherwise, it sends the\nsynchronous `OPEN` renew.\n\nThis preserves the existing asynchronous fast path when the wanted\ncaps are already issued, avoids changing cap-state semantics, and\nfixes the hang by guaranteeing that a stalled waiter eventually\nretries through a path that does not rely on the stale `mds_wanted`\nstate.\n\n[ idryomov: move CEPH_GET_CAPS_WAIT_TIMEOUT from libceph.h to\n  mds_client.h, formatting ]","Type":"Description","Title":"ceph: fix hanging __ceph_get_caps() with stale mds_wanted"}]}}}