From 1b23336ad98b3666c216617227c7767cd60a22be Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Mar 2009 12:55:52 -0700 Subject: [PATCH] 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 Tested-by: Milton Miller II Signed-off-by: Paul E. McKenney Cc: Manfred Spraul Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/idr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/idr.c b/lib/idr.c index c11c5765cdef..dab4bca86f5d 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -449,6 +449,7 @@ void idr_remove_all(struct idr *idp) n = idp->layers * IDR_BITS; p = idp->top; + rcu_assign_pointer(idp->top, NULL); max = 1 << n; id = 0; @@ -467,7 +468,6 @@ void idr_remove_all(struct idr *idp) p = *--paa; } } - rcu_assign_pointer(idp->top, NULL); idp->layers = 0; } EXPORT_SYMBOL(idr_remove_all); -- 2.39.5