lkml.org 
[lkml]   [2020]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v4 3/4] kdb: Make kdb_printf() console handling more robust
    Date
    While rounding up CPUs via NMIs, its possible that a rounded up CPU
    maybe holding a console port lock leading to kgdb master CPU stuck in
    a deadlock during invocation of console write operations. A similar
    deadlock could also be possible while using synchronous breakpoints.

    So in order to avoid such a deadlock, set oops_in_progress to encourage
    the console drivers to disregard their internal spin locks: in the
    current calling context the risk of deadlock is a bigger problem than
    risks due to re-entering the console driver. We operate directly on
    oops_in_progress rather than using bust_spinlocks() because the calls
    bust_spinlocks() makes on exit are not appropriate for this calling
    context.

    Suggested-by: Petr Mladek <pmladek@suse.com>
    Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
    ---
    kernel/debug/kdb/kdb_io.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
    index fad38eb..9e5a40d 100644
    --- a/kernel/debug/kdb/kdb_io.c
    +++ b/kernel/debug/kdb/kdb_io.c
    @@ -566,7 +566,18 @@ static void kdb_msg_write(char *msg, int msg_len)
    for_each_console(c) {
    if (!(c->flags & CON_ENABLED))
    continue;
    + /*
    + * Set oops_in_progress to encourage the console drivers to
    + * disregard their internal spin locks: in the current calling
    + * context the risk of deadlock is a bigger problem than risks
    + * due to re-entering the console driver. We operate directly on
    + * oops_in_progress rather than using bust_spinlocks() because
    + * the calls bust_spinlocks() makes on exit are not appropriate
    + * for this calling context.
    + */
    + ++oops_in_progress;
    c->write(c, msg, msg_len);
    + --oops_in_progress;
    touch_nmi_watchdog();
    }
    }
    --
    2.7.4
    \
     
     \ /
      Last update: 2020-05-29 13:28    [W:2.940 / U:0.280 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site