From: Andrew Morton Various people have reported machines failing to boot since pci_bus_sem was switched from a spinlock to an rwsem. The reason for this is that these people had "ide=" on the kernel commandline, and ide_setup() can end up calling PCI functions which do down_read(&pci_bus_sem). Ard has worked out the call tree: init/main.c start_kernel kernel/params.c parse_args("Booting kernel" kernel/params.c parse_one drivers/ide/ide.c ide_setup drivers/ide/ide.c init_ide_data drivers/ide/ide.c init_hwif_default include/asm-i386/ide.h ide_default_io_base(index) drivers/pci/search.c pci_find_device drivers/pci/search.c pci_find_subsys down_read(&pci_bus_sem); down_read() will unconditionally enable interrupts and some early interrupt (source unknown) comes in and whacks the machine, apparently because the LDT isn't set up yet. Cc: Ard -kwaak- van Breemen Cc: "Zhang, Yanmin" Cc: Chuck Ebbert <76306.1226@compuserve.com> Cc: Yinghai Lu Cc: Cc: Cc: "Eric W. Biederman" Cc: Greg KH Signed-off-by: Andrew Morton --- lib/rwsem-spinlock.c | 14 ++++++++------ 1 files changed, 8 insertions(+), 6 deletions(-) diff -puN lib/rwsem-spinlock.c~down_write-preserve-local-irqs lib/rwsem-spinlock.c --- a/lib/rwsem-spinlock.c~down_write-preserve-local-irqs +++ a/lib/rwsem-spinlock.c @@ -129,13 +129,14 @@ void fastcall __sched __down_read(struct { 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; } @@ -150,7 +151,7 @@ void fastcall __sched __down_read(struct 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 (;;) { @@ -195,13 +196,14 @@ void fastcall __sched __down_write_neste { 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; } @@ -216,7 +218,7 @@ void fastcall __sched __down_write_neste 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 (;;) { _