{"cve":"CVE-2022-48920","nvd":{"published":"2024-08-22T02:15:06.080","modified":"2026-06-17T05:16:37.080","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: get rid of warning on transaction commit when using flushoncommit\n\nWhen using the flushoncommit mount option, during almost every transaction\ncommit we trigger a warning from __writeback_inodes_sb_nr():\n\n  $ cat fs/fs-writeback.c:\n  (...)\n  static void __writeback_inodes_sb_nr(struct super_block *sb, ...\n  {\n        (...)\n        WARN_ON(!rwsem_is_locked(&sb->s_umount));\n        (...)\n  }\n  (...)\n\nThe trace produced in dmesg looks like the following:\n\n  [947.473890] WARNING: CPU: 5 PID: 930 at fs/fs-writeback.c:2610 __writeback_inodes_sb_nr+0x7e/0xb3\n  [947.481623] Modules linked in: nfsd nls_cp437 cifs asn1_decoder cifs_arc4 fscache cifs_md4 ipmi_ssif\n  [947.489571] CPU: 5 PID: 930 Comm: btrfs-transacti Not tainted 95.16.3-srb-asrock-00001-g36437ad63879 #186\n  [947.497969] RIP: 0010:__writeback_inodes_sb_nr+0x7e/0xb3\n  [947.502097] Code: 24 10 4c 89 44 24 18 c6 (...)\n  [947.519760] RSP: 0018:ffffc90000777e10 EFLAGS: 00010246\n  [947.523818] RAX: 0000000000000000 RBX: 0000000000963300 RCX: 0000000000000000\n  [947.529765] RDX: 0000000000000000 RSI: 000000000000fa51 RDI: ffffc90000777e50\n  [947.535740] RBP: ffff888101628a90 R08: ffff888100955800 R09: ffff888100956000\n  [947.541701] R10: 0000000000000002 R11: 0000000000000001 R12: ffff888100963488\n  [947.547645] R13: ffff888100963000 R14: ffff888112fb7200 R15: ffff888100963460\n  [947.553621] FS:  0000000000000000(0000) GS:ffff88841fd40000(0000) knlGS:0000000000000000\n  [947.560537] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n  [947.565122] CR2: 0000000008be50c4 CR3: 000000000220c000 CR4: 00000000001006e0\n  [947.571072] Call Trace:\n  [947.572354]  <TASK>\n  [947.573266]  btrfs_commit_transaction+0x1f1/0x998\n  [947.576785]  ? start_transaction+0x3ab/0x44e\n  [947.579867]  ? schedule_timeout+0x8a/0xdd\n  [947.582716]  transaction_kthread+0xe9/0x156\n  [947.585721]  ? btrfs_cleanup_transaction.isra.0+0x407/0x407\n  [947.590104]  kthread+0x131/0x139\n  [947.592168]  ? set_kthread_struct+0x32/0x32\n  [947.595174]  ret_from_fork+0x22/0x30\n  [947.597561]  </TASK>\n  [947.598553] ---[ end trace 644721052755541c ]---\n\nThis is because we started using writeback_inodes_sb() to flush delalloc\nwhen committing a transaction (when using -o flushoncommit), in order to\navoid deadlocks with filesystem freeze operations. This change was made\nby commit ce8ea7cc6eb313 (\"btrfs: don't call btrfs_start_delalloc_roots\nin flushoncommit\"). After that change we started producing that warning,\nand every now and then a user reports this since the warning happens too\noften, it spams dmesg/syslog, and a user is unsure if this reflects any\nproblem that might compromise the filesystem's reliability.\n\nWe can not just lock the sb->s_umount semaphore before calling\nwriteback_inodes_sb(), because that would at least deadlock with\nfilesystem freezing, since at fs/super.c:freeze_super() sync_filesystem()\nis called while we are holding that semaphore in write mode, and that can\ntrigger a transaction commit, resulting in a deadlock. It would also\ntrigger the same type of deadlock in the unmount path. Possibly, it could\nalso introduce some other locking dependencies that lockdep would report.\n\nTo fix this call try_to_writeback_inodes_sb() instead of\nwriteback_inodes_sb(), because that will try to read lock sb->s_umount\nand then will only call writeback_inodes_sb() if it was able to lock it.\nThis is fine because the cases where it can't read lock sb->s_umount\nare during a filesystem unmount or during a filesystem freeze - in those\ncases sb->s_umount is write locked and sync_filesystem() is called, which\ncalls writeback_inodes_sb(). In other words, in all cases where we can't\ntake a read lock on sb->s_umount, writeback is already being triggered\nelsewhere.\n\nAn alternative would be to call btrfs_start_delalloc_roots() with a\nnumber of pages different from LONG_MAX, for example matching the number\nof delalloc bytes we currently have, in \n---truncated---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":["CWE-667"],"references":["https://git.kernel.org/stable/c/850a77c999b81dd2724efd2684068d6f90db8c16","https://git.kernel.org/stable/c/a0f0cf8341e34e5d2265bfd3a7ad68342da1e2aa","https://git.kernel.org/stable/c/e4d044dbffcd570351f21c747fc77ff90aed7f2e"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:54:16.205165117+00:00"},"epss":{"cve":"CVE-2022-48920","score":0.00164,"percentile":0.05623,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}