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hotplug: Prevent alloc/free of irq descriptors during cpu up/down

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When a cpu goes up some architectures (e.g. x86) have to walk the irq
space to set up the vector space for the cpu. While this needs extra
protection at the architecture level we can avoid a few race
conditions by preventing the concurrent allocation/free of irq
descriptors and the associated data.

When a cpu goes down it moves the interrupts which are targeted to
this cpu away by reassigning the affinities. While this happens
interrupts can be allocated and freed, which opens a can of race
conditions in the code which reassignes the affinities because
interrupt descriptors might be freed underneath.

Example:

CPU1				CPU2
cpu_up/down
 irq_desc = irq_to_desc(irq);
				remove_from_radix_tree(desc);
 raw_spin_lock(&desc->lock);
				free(desc);

We could protect the irq descriptors with RCU, but that would require
a full tree change of all accesses to interrupt descriptors. But
fortunately these kind of race conditions are rather limited to a few
things like cpu hotplug. The normal setup/teardown is very well
serialized. So the simpler and obvious solution is:

Prevent allocation and freeing of interrupt descriptors accross cpu
hotplug.

Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: xiao jin <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Yanmin Zhang <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
This commit is contained in:
Thomas Gleixner 2015-07-05 17:12:30 +00:00
commit a899418167
3 changed files with 27 additions and 6 deletions
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4
kernel/irq/internals.h
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@ -76,12 +76,8 @@ extern void unmask_threaded_irq(struct irq_desc *desc);
#ifdef CONFIG_SPARSE_IRQ
static inline void irq_mark_irq(unsigned int irq) { }
extern void irq_lock_sparse(void);
extern void irq_unlock_sparse(void);
#else
extern void irq_mark_irq(unsigned int irq);
static inline void irq_lock_sparse(void) { }
static inline void irq_unlock_sparse(void) { }
#endif
extern void init_kstat_irqs(struct irq_desc *desc, int node, int nr);