Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: > On Wed, 31 Mar 2010, H. Peter Anvin wrote: >> >> The obvious way to fix this would be to use >> spin_lock_irqsave..spin_lock_irqrestore in __down_read as well as in the >> other locations; I don't have a good feel for what the cost of doing so >> would be, though. On x86 it's fairly expensive simply because the only >> way to save the state is to push it on the stack, which the compiler >> doesn't deal well with, but this code isn't used on x86. > [...] > So making the slow-path do the spin_[un]lock_irq{save,restore}() versions > sounds like the right thing. It won't be a performance issue: it _is_ the > slow-path, and we're already doing the expensive part (the spinlock itself > and the irq thing). > > So ACK on the idea. Who wants to write the trivial patch and test it? OK, I'll bite since I was seeing boot-time hangs on ARM (TI OMAP3) due to this. Patch below. Kevin >From 7baff4008353bbfd2a2e2a4da22b87bc4efa4194 Mon Sep 17 00:00:00 2001 From: Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx> Date: Wed, 7 Apr 2010 11:52:46 -0700 Subject: [PATCH] rwsem generic spinlock: use IRQ save/restore spinlocks rwsems can be used with IRQs disabled, particularily in early boot before IRQs are enabled. Currently the spin_unlock_irq() usage in the slow-patch will unconditionally enable interrupts and cause problems since interrupts are not yet initialized or enabled. This patch uses save/restore versions of IRQ spinlocks in the slowpath to ensure interrupts are not unintentionally disabled. Signed-off-by: Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx> --- lib/rwsem-spinlock.c | 14 ++++++++------ 1 files changed, 8 insertions(+), 6 deletions(-) diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c index ccf95bf..ffc9fc7 100644 --- a/lib/rwsem-spinlock.c +++ b/lib/rwsem-spinlock.c @@ -143,13 +143,14 @@ void __sched __down_read(struct rw_semaphore *sem) { struct rwsem_waiter waiter; struct task_struct *tsk; + unsigned long flags; - spin_lock_irq(&sem->wait_lock); + spin_lock_irqsave(&sem->wait_lock, flags); if (sem->activity >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity++; - spin_unlock_irq(&sem->wait_lock); + spin_unlock_irqrestore(&sem->wait_lock, flags); goto out; } @@ -164,7 +165,7 @@ void __sched __down_read(struct rw_semaphore *sem) list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ - spin_unlock_irq(&sem->wait_lock); + spin_unlock_irqrestore(&sem->wait_lock, flags); /* wait to be given the lock */ for (;;) { @@ -209,13 +210,14 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass) { struct rwsem_waiter waiter; struct task_struct *tsk; + unsigned long flags; - spin_lock_irq(&sem->wait_lock); + spin_lock_irqsave(&sem->wait_lock, flags); if (sem->activity == 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity = -1; - spin_unlock_irq(&sem->wait_lock); + spin_unlock_irqrestore(&sem->wait_lock, flags); goto out; } @@ -230,7 +232,7 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass) list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ - spin_unlock_irq(&sem->wait_lock); + spin_unlock_irqrestore(&sem->wait_lock, flags); /* wait to be given the lock */ for (;;) { -- 1.7.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html