DragonFly commits List (threaded) for 2011-11
git: kernel - Fix pmap->pm_active race in switch code
Author: Matthew Dillon <email@example.com>
Date: Wed Nov 30 17:29:35 2011 -0800
kernel - Fix pmap->pm_active race in switch code
* Use an atomic cmpxchg to set the cpu bit in the pmap->pm_active bitmap
AND test the pmap interlock bit at the same time, instead of testing
the interlock bit afterwords.
* In addition, if we find the lock bit set and must spin-wait for it to
clear, we skip the %cr3 comparison check and unconditionally load %cr3.
* It is unclear if the race could be realized in any way. It was probably
not responsible for the seg-fault issue as prior tests with an unconditional
load of %cr3 did not fix the problem. Plus in the same-%cr3-as-last-thread
case the cpu bit is already set so there should be no possibility of
losing a TLB interlock IPI (and %cr3 is loaded unconditionally when it
doesn't match, so....).
But fix the race anyway.
Summary of changes:
sys/platform/pc32/i386/swtch.s | 33 ++++++++++++++---
sys/platform/pc64/x86_64/swtch.s | 70 ++++++++++++++++++++++++++-----------
2 files changed, 76 insertions(+), 27 deletions(-)
DragonFly BSD source repository