lkml.org 
[lkml]   [2010]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    SubjectRe: start_kernel(): bug: interrupts were enabled early
    From
    Date
    Linus Torvalds <torvalds@linux-foundation.org> 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@deeprootsystems.com>
    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@deeprootsystems.com>
    ---
    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


    \
     
     \ /
      Last update: 2010-04-07 21:11    [W:0.024 / U:0.776 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site