{ "containers": { "cna": { "providerMetadata": { "orgId": "f4215fc3-5b6b-47ff-a258-f7189bd81038" }, "descriptions": [ { "lang": "en", "value": "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] \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] \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---" } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/btrfs/transaction.c" ], "versions": [ { "version": "1da177e4c3f4", "lessThan": "850a77c999b8", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f4", "lessThan": "e4d044dbffcd", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f4", "lessThan": "a0f0cf8341e3", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/btrfs/transaction.c" ], "versions": [ { "version": "5.15.27", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.16.13", "lessThanOrEqual": "5.16.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.17", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/850a77c999b81dd2724efd2684068d6f90db8c16" }, { "url": "https://git.kernel.org/stable/c/e4d044dbffcd570351f21c747fc77ff90aed7f2e" }, { "url": "https://git.kernel.org/stable/c/a0f0cf8341e34e5d2265bfd3a7ad68342da1e2aa" } ], "title": "btrfs: get rid of warning on transaction commit when using flushoncommit", "x_generator": { "engine": "bippy-c9c4e1df01b2" } } }, "cveMetadata": { "assignerOrgId": "f4215fc3-5b6b-47ff-a258-f7189bd81038", "cveID": "CVE-2022-48920", "requesterUserId": "gregkh@kernel.org", "serial": "1", "state": "PUBLISHED" }, "dataType": "CVE_RECORD", "dataVersion": "5.0" }