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We actually have two separate bad bugs
1. The read_lock implementation spins with disabled interrupts. This is
completely wrong
2. Our spin_lock_irqsave should check to see if interrupts were enabled
before the call and re-enable interrupts around the inner spin loop.
The problem is that if we spin with interrupts off, we can't receive
IPIs. This has resulted in a bug where SMP machines suddenly spit
smp_call_function timeout messages and hang.
The scenario I've caught is
CPU0 does a flush_tlb_all holding the vmlist_lock for write.
CPU1 tries a cat of /proc/meminfo which tries to acquire vmlist_lock for
read
CPU1 is now spinning with interrupts disabled
CPU0 tries to execute a smp_call_function to flush the local tlb caches
This is now a deadlock because CPU1 is spinning with interrupts disabled
and can never receive the IPI
Signed-off-by: James Bottomley <jejb@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
08dc2ca61e