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![Ingo Molnar](/assets/img/avatar_default.png)
This patch (written by me and also containing many suggestions of Arjan van de Ven) does a major cleanup of the spinlock code. It does the following things: - consolidates and enhances the spinlock/rwlock debugging code - simplifies the asm/spinlock.h files - encapsulates the raw spinlock type and moves generic spinlock features (such as ->break_lock) into the generic code. - cleans up the spinlock code hierarchy to get rid of the spaghetti. Most notably there's now only a single variant of the debugging code, located in lib/spinlock_debug.c. (previously we had one SMP debugging variant per architecture, plus a separate generic one for UP builds) Also, i've enhanced the rwlock debugging facility, it will now track write-owners. There is new spinlock-owner/CPU-tracking on SMP builds too. All locks have lockup detection now, which will work for both soft and hard spin/rwlock lockups. The arch-level include files now only contain the minimally necessary subset of the spinlock code - all the rest that can be generalized now lives in the generic headers: include/asm-i386/spinlock_types.h | 16 include/asm-x86_64/spinlock_types.h | 16 I have also split up the various spinlock variants into separate files, making it easier to see which does what. The new layout is: SMP | UP ----------------------------|----------------------------------- asm/spinlock_types_smp.h | linux/spinlock_types_up.h linux/spinlock_types.h | linux/spinlock_types.h asm/spinlock_smp.h | linux/spinlock_up.h linux/spinlock_api_smp.h | linux/spinlock_api_up.h linux/spinlock.h | linux/spinlock.h /* * here's the role of the various spinlock/rwlock related include files: * * on SMP builds: * * asm/spinlock_types.h: contains the raw_spinlock_t/raw_rwlock_t and the * initializers * * linux/spinlock_types.h: * defines the generic type and initializers * * asm/spinlock.h: contains the __raw_spin_*()/etc. lowlevel * implementations, mostly inline assembly code * * (also included on UP-debug builds:) * * linux/spinlock_api_smp.h: * contains the prototypes for the _spin_*() APIs. * * linux/spinlock.h: builds the final spin_*() APIs. * * on UP builds: * * linux/spinlock_type_up.h: * contains the generic, simplified UP spinlock type. * (which is an empty structure on non-debug builds) * * linux/spinlock_types.h: * defines the generic type and initializers * * linux/spinlock_up.h: * contains the __raw_spin_*()/etc. version of UP * builds. (which are NOPs on non-debug, non-preempt * builds) * * (included on UP-non-debug builds:) * * linux/spinlock_api_up.h: * builds the _spin_*() APIs. * * linux/spinlock.h: builds the final spin_*() APIs. */ All SMP and UP architectures are converted by this patch. arm, i386, ia64, ppc, ppc64, s390/s390x, x64 was build-tested via crosscompilers. m32r, mips, sh, sparc, have not been tested yet, but should be mostly fine. From: Grant Grundler <grundler@parisc-linux.org> Booted and lightly tested on a500-44 (64-bit, SMP kernel, dual CPU). Builds 32-bit SMP kernel (not booted or tested). I did not try to build non-SMP kernels. That should be trivial to fix up later if necessary. I converted bit ops atomic_hash lock to raw_spinlock_t. Doing so avoids some ugly nesting of linux/*.h and asm/*.h files. Those particular locks are well tested and contained entirely inside arch specific code. I do NOT expect any new issues to arise with them. If someone does ever need to use debug/metrics with them, then they will need to unravel this hairball between spinlocks, atomic ops, and bit ops that exist only because parisc has exactly one atomic instruction: LDCW (load and clear word). From: "Luck, Tony" <tony.luck@intel.com> ia64 fix Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Arjan van de Ven <arjanv@infradead.org> Signed-off-by: Grant Grundler <grundler@parisc-linux.org> Cc: Matthew Wilcox <willy@debian.org> Signed-off-by: Hirokazu Takata <takata@linux-m32r.org> Signed-off-by: Mikael Pettersson <mikpe@csd.uu.se> Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
208 lines
4.5 KiB
C
208 lines
4.5 KiB
C
/*
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* lib/kernel_lock.c
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*
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* This is the traditional BKL - big kernel lock. Largely
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* relegated to obsolescense, but used by various less
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* important (or lazy) subsystems.
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*/
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#include <linux/smp_lock.h>
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#include <linux/module.h>
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#include <linux/kallsyms.h>
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#ifdef CONFIG_PREEMPT_BKL
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/*
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* The 'big kernel semaphore'
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*
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* This mutex is taken and released recursively by lock_kernel()
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* and unlock_kernel(). It is transparently dropped and reaquired
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* over schedule(). It is used to protect legacy code that hasn't
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* been migrated to a proper locking design yet.
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*
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* Note: code locked by this semaphore will only be serialized against
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* other code using the same locking facility. The code guarantees that
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* the task remains on the same CPU.
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*
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* Don't use in new code.
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*/
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static DECLARE_MUTEX(kernel_sem);
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/*
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* Re-acquire the kernel semaphore.
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*
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* This function is called with preemption off.
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*
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* We are executing in schedule() so the code must be extremely careful
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* about recursion, both due to the down() and due to the enabling of
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* preemption. schedule() will re-check the preemption flag after
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* reacquiring the semaphore.
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*/
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int __lockfunc __reacquire_kernel_lock(void)
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{
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struct task_struct *task = current;
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int saved_lock_depth = task->lock_depth;
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BUG_ON(saved_lock_depth < 0);
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task->lock_depth = -1;
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preempt_enable_no_resched();
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down(&kernel_sem);
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preempt_disable();
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task->lock_depth = saved_lock_depth;
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return 0;
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}
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void __lockfunc __release_kernel_lock(void)
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{
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up(&kernel_sem);
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}
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/*
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* Getting the big kernel semaphore.
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*/
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void __lockfunc lock_kernel(void)
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{
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struct task_struct *task = current;
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int depth = task->lock_depth + 1;
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if (likely(!depth))
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/*
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* No recursion worries - we set up lock_depth _after_
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*/
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down(&kernel_sem);
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task->lock_depth = depth;
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}
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void __lockfunc unlock_kernel(void)
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{
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struct task_struct *task = current;
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BUG_ON(task->lock_depth < 0);
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if (likely(--task->lock_depth < 0))
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up(&kernel_sem);
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}
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#else
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/*
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* The 'big kernel lock'
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*
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* This spinlock is taken and released recursively by lock_kernel()
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* and unlock_kernel(). It is transparently dropped and reaquired
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* over schedule(). It is used to protect legacy code that hasn't
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* been migrated to a proper locking design yet.
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*
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* Don't use in new code.
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*/
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static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag);
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/*
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* Acquire/release the underlying lock from the scheduler.
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*
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* This is called with preemption disabled, and should
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* return an error value if it cannot get the lock and
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* TIF_NEED_RESCHED gets set.
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*
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* If it successfully gets the lock, it should increment
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* the preemption count like any spinlock does.
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*
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* (This works on UP too - _raw_spin_trylock will never
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* return false in that case)
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*/
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int __lockfunc __reacquire_kernel_lock(void)
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{
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while (!_raw_spin_trylock(&kernel_flag)) {
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if (test_thread_flag(TIF_NEED_RESCHED))
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return -EAGAIN;
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cpu_relax();
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}
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preempt_disable();
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return 0;
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}
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void __lockfunc __release_kernel_lock(void)
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{
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_raw_spin_unlock(&kernel_flag);
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preempt_enable_no_resched();
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}
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/*
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* These are the BKL spinlocks - we try to be polite about preemption.
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* If SMP is not on (ie UP preemption), this all goes away because the
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* _raw_spin_trylock() will always succeed.
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*/
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#ifdef CONFIG_PREEMPT
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static inline void __lock_kernel(void)
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{
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preempt_disable();
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if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
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/*
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* If preemption was disabled even before this
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* was called, there's nothing we can be polite
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* about - just spin.
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*/
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if (preempt_count() > 1) {
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_raw_spin_lock(&kernel_flag);
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return;
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}
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/*
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* Otherwise, let's wait for the kernel lock
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* with preemption enabled..
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*/
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do {
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preempt_enable();
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while (spin_is_locked(&kernel_flag))
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cpu_relax();
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preempt_disable();
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} while (!_raw_spin_trylock(&kernel_flag));
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}
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}
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#else
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/*
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* Non-preemption case - just get the spinlock
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*/
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static inline void __lock_kernel(void)
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{
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_raw_spin_lock(&kernel_flag);
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}
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#endif
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static inline void __unlock_kernel(void)
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{
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spin_unlock(&kernel_flag);
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}
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/*
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* Getting the big kernel lock.
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*
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* This cannot happen asynchronously, so we only need to
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* worry about other CPU's.
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*/
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void __lockfunc lock_kernel(void)
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{
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int depth = current->lock_depth+1;
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if (likely(!depth))
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__lock_kernel();
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current->lock_depth = depth;
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}
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void __lockfunc unlock_kernel(void)
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{
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BUG_ON(current->lock_depth < 0);
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if (likely(--current->lock_depth < 0))
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__unlock_kernel();
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}
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#endif
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EXPORT_SYMBOL(lock_kernel);
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EXPORT_SYMBOL(unlock_kernel);
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