Messages in this thread Patch in this message | | | From | Sumit Garg <> | Subject | [PATCH v4 3/4] kdb: Make kdb_printf() console handling more robust | Date | Fri, 29 May 2020 16:56:46 +0530 |
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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
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