I got an oops on v5.0.7-rt5 (due to kexec code not properly checking for disabled EFI, patch coming) and after the primary oops, I got this: [ 111.575331] 055: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004 [ 111.584457] 055: in_atomic(): 0, irqs_disabled(): 1, pid: 13289, name: kexec [ 111.591502] 055: INFO: lockdep is turned off. [ 111.595862] 055: irq event stamp: 481304 [ 111.599786] 055: hardirqs last enabled at (481303): [<ffffffff811853b0>] ktime_get_coarse_real_ts64+0x60/0xc0 [ 111.609779] 055: hardirqs last disabled at (481304): [<ffffffff81001ea1>] trace_hardirqs_off_thunk+0x1a/0x1c [ 111.619599] 055: softirqs last enabled at (0): [<ffffffff810d13e3>] copy_process.part.30+0x833/0x2680 [ 111.628900] 055: softirqs last disabled at (0): [<0000000000000000>] (null) [ 111.636723] 055: CPU: 55 PID: 13289 Comm: kexec Tainted: G D E 5.0.7-rt5+ #3 [ 111.644896] 055: Hardware name: Intel Corporation S2600BT/S2600BT, BIOS SE5C620.86B.01.00.0763.022420181017 02/24/2018 [ 111.655582] 055: Call Trace: [ 111.658468] 055: dump_stack+0x5e/0x8b [ 111.662223] 055: ___might_sleep+0x177/0x1e0 [ 111.666494] 055: __rt_mutex_lock_state+0x1f/0x80 [ 111.671202] 055: kmsg_dump+0x88/0x160 [ 111.674951] 055: ? kmsg_dump+0x1f/0x160 [ 111.678880] 055: oops_end+0x59/0xd0 [ 111.682459] 055: no_context+0x185/0x540 [ 111.686383] 055: ? __do_page_fault+0x1da/0x530 [ 111.690918] 055: do_page_fault+0x2d/0x290 [ 111.695017] 055: page_fault+0x1e/0x30 [ 111.698769] 055: RIP: 0010: (null) [ 111.702956] 055: Code: Bad RIP value. [ 111.706618] 055: RSP: 0018:ffffc900754d3ea8 EFLAGS: 00010246 [ 111.712278] 055: [ 111.714213] 055: RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffc900754d3eb8 [ 111.721777] 055: RDX: 0000000000000000 RSI: ffffc900754d3ec0 RDI: ffffc900754d3ed2 [ 111.729342] 055: RBP: ffffc900754d3ef8 R08: ffffc900754d3eb7 R09: 0000000000000000 [ 111.736910] 055: R10: 0000000000000000 R11: 0000000000000005 R12: 0000000000e84950 [ 111.744476] 055: R13: 0000000037f54730 R14: 0000000000000000 R15: 0000000000000000 [ 111.752045] 055: ? arch_ima_get_secureboot+0x11e/0x190 [ 111.757269] 055: ? selinux_kernel_read_file+0x20/0x20 [ 111.762406] 055: ? ima_load_data+0x46/0xa0 [ 111.766593] 055: ? __x64_sys_kexec_load+0x44/0xd0 [ 111.771384] 055: ? do_syscall_64+0x5a/0x260 [ 111.775657] 055: ? entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 111.791742] 055: RIP: 0010: (null) [ 111.795930] 055: Code: Bad RIP value. [ 111.799595] 055: RSP: 0018:ffffc900754d3ea8 EFLAGS: 00010246 [ 111.805254] 055: [ 111.807185] 055: RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffc900754d3eb8 [ 111.814750] 055: RDX: 0000000000000000 RSI: ffffc900754d3ec0 RDI: ffffc900754d3ed2 [ 111.822309] 055: RBP: ffffc900754d3ef8 R08: ffffc900754d3eb7 R09: 0000000000000000 [ 111.829873] 055: R10: 0000000000000000 R11: 0000000000000005 R12: 0000000000e84950 [ 111.837440] 055: R13: 0000000037f54730 R14: 0000000000000000 R15: 0000000000000000 [ 111.845008] 055: FS: 00007fe31bffa740(0000) GS:ffff8897de200000(0000) knlGS:0000000000000000 [ 111.853525] 055: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 111.859704] 055: CR2: ffffffffffffffd6 CR3: 00000017d47da004 CR4: 00000000007606e0 [ 111.867272] 055: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 111.874837] 055: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 111.882401] 055: PKRU: 55555554 [ 111.885540] 055: Kernel panic - not syncing: Fatal exception [ 111.891314] 055: Kernel Offset: disabled ...plus a bunch of "unexpected reschedule of offline CPU" messages. kmsg_dump() calls kmsg_dump_rewind(), which calls mutex_lock(). This would be broken even on non-RT. It's not clear what kmsg_dump_lock is even supposed to be protecting -- kmsg_dump_get_buffer() does not take the lock, and the only caller to the locked version of kmsg_dump_get_line() is in arch/um/kernel/kmsg_dump.c. -Scott
