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author | Peter Zijlstra | 2016-05-20 18:04:36 +0200 |
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committer | Linus Torvalds | 2016-05-20 19:30:32 -0700 |
commit | 54cf809b9512be95f53ed4a5e3b631d1ac42f0fa (patch) | |
tree | eeeeb69b689c041b08741bd97ea23872020c48d3 /drivers/clk/clk-clps711x.c | |
parent | b99a9e8776ca837344c6b64d518483fc5d5eefb4 (diff) |
locking,qspinlock: Fix spin_is_locked() and spin_unlock_wait()
Similar to commits:
51d7d5205d33 ("powerpc: Add smp_mb() to arch_spin_is_locked()")
d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers")
qspinlock suffers from the fact that the _Q_LOCKED_VAL store is
unordered inside the ACQUIRE of the lock.
And while this is not a problem for the regular mutual exclusive
critical section usage of spinlocks, it breaks creative locking like:
spin_lock(A) spin_lock(B)
spin_unlock_wait(B) if (!spin_is_locked(A))
do_something() do_something()
In that both CPUs can end up running do_something at the same time,
because our _Q_LOCKED_VAL store can drop past the spin_unlock_wait()
spin_is_locked() loads (even on x86!!).
To avoid making the normal case slower, add smp_mb()s to the less used
spin_unlock_wait() / spin_is_locked() side of things to avoid this
problem.
Reported-and-tested-by: Davidlohr Bueso <dave@stgolabs.net>
Reported-by: Giovanni Gherdovich <ggherdovich@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org # v4.2 and later
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/clk/clk-clps711x.c')
0 files changed, 0 insertions, 0 deletions