• Soumya PN's avatar
    ftrace: Don't disable irqs when taking the tasklist_lock read_lock · 6112a300
    Soumya PN authored
    In ftrace.c inside the function alloc_retstack_tasklist() (which will be
    invoked when function_graph tracing is on) the tasklist_lock is being
    held as reader while iterating through a list of threads. Here the lock
    is being held as reader with irqs disabled. The tasklist_lock is never
    write_locked in interrupt context so it is safe to not disable interrupts
    for the duration of read_lock in this block which, can be significant,
    given the block of code iterates through all threads. Hence changing the
    code to call read_lock() and read_unlock() instead of read_lock_irqsave()
    and read_unlock_irqrestore().
    
    A similar change was made in commits: 8063e41d ("tracing: Change
    syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()")'
    and 3472eaa1 ("sched: normalize_rt_tasks(): Don't use _irqsave for
    tasklist_lock, use task_rq_lock()")'
    
    Link: http://lkml.kernel.org/r/1463500874-77480-1-git-send-email-soumya.p.n@hpe.comSigned-off-by: default avatarSoumya PN <soumya.p.n@hpe.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    6112a300
ftrace.c 139 KB