idr: make idr_remove_all() do removal -before- free_layer()
Fix a problem in the IDR system, where an idr_remove_all() hands a data element to call_rcu() (via free_layer()) before making that data element inaccessible to new readers. This is very bad, and results in readers still having a reference to this data element at the end of the grace period. Tests on large machines that concurrently map and unmap user-space memory within the same multithreaded process result in crashes within about five minutes. Applying this patch increases the kernel's longevity to the three-to-eight-hour range. There appear to be other similar problems in idr_get_empty_slot() and sub_remove(), but I fixed the easy one in idr_remove_all() first. It is therefore no surprise that failures still occur. Located-by: Milton Miller II <miltonm@austin.ibm.com> Tested-by: Milton Miller II <miltonm@austin.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -449,6 +449,7 @@ void idr_remove_all(struct idr *idp)
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n = idp->layers * IDR_BITS;
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p = idp->top;
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rcu_assign_pointer(idp->top, NULL);
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max = 1 << n;
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id = 0;
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@ -467,7 +468,6 @@ void idr_remove_all(struct idr *idp)
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p = *--paa;
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}
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}
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rcu_assign_pointer(idp->top, NULL);
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idp->layers = 0;
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}
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EXPORT_SYMBOL(idr_remove_all);
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