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authorSumit Garg <sumit.garg@linaro.org>2020-06-04 15:31:18 +0530
committerDaniel Thompson <daniel.thompson@linaro.org>2020-06-25 12:04:30 +0100
commit2a78b85b70f9c3d450619d369d349ba861320510 (patch)
tree72e6d16d654de42d03100d53b9a86eb54e3994ea /kernel/debug/kdb
parente8857288bb620d594c94a219148d18562e52b06e (diff)
kdb: Make kdb_printf() console handling more robust
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: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Reviewed-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/1591264879-25920-4-git-send-email-sumit.garg@linaro.org Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Diffstat (limited to 'kernel/debug/kdb')
-rw-r--r--kernel/debug/kdb/kdb_io.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 58b7d256d0a4..0e4f2eda96d8 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -562,7 +562,18 @@ static void kdb_msg_write(const 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();
}
}

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