[LU-17540] sync and delay before LBUG() calls panic()

• Type: Improvement
• Resolution: Unresolved
• Priority: Minor
• Labels: easy lug24dd
• Severity: 3
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

It would be useful to have a few second pause between when LBUG() is called and panic() is triggered, in order for the stack trace to be written to the serial console, and ideally also to give a chance for it to be written to /var/log/messages if no serial console is available.

The code currently calls panic() immediately after dumping the stack:

lbug_with_loc(struct libcfs_debug_msg_data *msgdata)
{
        libcfs_catastrophe = 1;
        libcfs_debug_msg(msgdata, "LBUG\n");

        if (in_interrupt()) {
                panic("LBUG in interrupt.\n");
                /* not reached */
        }

        libcfs_debug_dumpstack(NULL);
        if (libcfs_panic_on_lbug)
                panic("LBUG");
        else
                libcfs_debug_dumplog();
        set_current_state(TASK_UNINTERRUPTIBLE);
        while (1)
                schedule();
}

It would be reasonable to allow libcfs_panic_on_lbug() to store the number of seconds (or milliseconds?) to delay before calling panic(), probably using msleep() to busy-wait instead of being scheduled. In the meantime, a task could be dispatched to a work queue to try sync-and-flush for whatever can be written during this delay (if the system is not locked up), equivalent to "sysrq-w" and "sysrq-s".

Issue Links

• is related to: LU-16297 ptl_send_rpc() ASSERTION ( (at_max == 0) || imp->imp_state != LUSTRE_IMP_FULL || (imp->imp_msghdr_flags & MSGHDR_AT_SUPPORT) || !(imp->imp_connect_data.ocd_connect_flags & 0x1000000ULL) )
• is related to: LU-16375 dump more information for threads blocked on local DLM locks
• is related to: LU-16625 improved Lustre thread debugging