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authorRalf Baechle <ralf@linux-mips.org>2005-02-10 12:00:06 +0000
committerRalf Baechle <ralf@linux-mips.org>2005-10-29 19:30:30 +0100
commit57f0060b8a2bb2a70a4cce1a37d5e0158cea92a6 (patch)
treef2cca6d9bc63b4f180739e9f2a86db0f0e2d7d86 /arch/mips/kernel/smp.c
parent26852d5cdb2bac01f2a48b815194a045e8a8e300 (diff)
Document why calling smp_call_function will deadlock when called with
interrupts disabled. Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch/mips/kernel/smp.c')
-rw-r--r--arch/mips/kernel/smp.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index af5cd3b8a396..1d3a4b501949 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -121,7 +121,19 @@ struct call_data_struct *call_data;
* or are or have executed.
*
* You must not call this function with disabled interrupts or from a
- * hardware interrupt handler or from a bottom half handler.
+ * hardware interrupt handler or from a bottom half handler:
+ *
+ * CPU A CPU B
+ * Disable interrupts
+ * smp_call_function()
+ * Take call_lock
+ * Send IPIs
+ * Wait for all cpus to acknowledge IPI
+ * CPU A has not responded, spin waiting
+ * for cpu A to respond, holding call_lock
+ * smp_call_function()
+ * Spin waiting for call_lock
+ * Deadlock Deadlock
*/
int smp_call_function (void (*func) (void *info), void *info, int retry,
int wait)

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