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2011-10-10 14:46:21
| 140 # userspace resumption stub bypassing syscall exit tracing 141 ALIGN 142 ret_from_exception: 143 preempt_stop 在抢占打开的情况下，上面的语句只是关闭当前cpu的中断。不仔细看，此处可能和下面cli重复，其实不然，这保证了此处到下面的cli之间进程不被抢占。 144 ret_from_intr: 145 GET_THREAD_INFO(%ebp) 146 movl EFLAGS(%esp), %eax # mix EFLAGS and CS 147 movb CS(%esp), %al 取得当前进程的一些信息，其中包括EFLAGS和CS 148 testl $(VM_MASK | 3), %eax 测试系统进入中断或者是异常的时候是否是用户空间 149 jz resume_kernel 如果不是将跳转到resume_kernel继续执行 150 ENTRY(resume_userspace) 151 cli # make sure we don't miss an interrupt 152 # setting need_resched or sigpending 153 # between sampling and the iret 154 movl TI_flags(%ebp), %ecx 155 andl $_TIF_WORK_MASK, %ecx # is there any work to be done on 156 # int/exception return? 157 jne work_pending 158 jmp restore_all 159 160 #ifdef CONFIG_PREEMPT 161 ENTRY(resume_kernel) 162 cli 关闭中断 163 cmpl $0,TI_preempt_count(%ebp) # non-zero preempt_count ? 测试当前的抢占计数器是否为零，只有为零的时候才允许调度。 164 jnz restore_nocheck 不为零，不进行调度，这个时候很可能是此进程持有某个锁，处于临界区，或者说是原子上下文中，比如说他返回的是软中断上下文，或者是中断嵌套中的上一级中断。 165 need_resched: 166 movl TI_flags(%ebp), %ecx # need_resched set ? 167 testb $_TIF_NEED_RESCHED, %cl 168 jz restore_all 测试当前进程的需要被重新调度位是否设置，如果没有设置不进行调度。 169 testl $IF_MASK,EFLAGS(%esp) # interrupts off (exception path) ? 170 jz restore_all 测试当前进程在进入中断之前，中断是否是开着的。有人可能问了，关了中断，他就不能走到这步了。其实不然，我们不要忘记了那些不可屏蔽的中断，或者称他们为异常，他们即使是在关闭中断的条件下，仍然可能跑到这里。但是为什么开着中断的情况下引起的异常是能够引起调度的？因为，这表明那个程序没有处于原子上下文，所以，还是可以安全地被调度的。 171 call preempt_schedule_irq 运行调度程序 172 jmp need_resched 再次测试是否需要调度 173 #endif |
| 3174 /* 3175 * this is is the entry point to schedule() from kernel preemption 3176 * off of irq context. 3177 * Note, that this is called and return with irqs disabled. This will 3178 * protect us against recursive calling from irq. 3179 */ 3180 asmlinkage void __sched preempt_schedule_irq(void) 3181 { 3182 struct thread_info *ti = current_thread_info(); 3183 #ifdef CONFIG_PREEMPT_BKL 3184 struct task_struct *task = current; 3185 int saved_lock_depth; 3186 #endif 3187 /* Catch callers which need to be fixed*/ 3188 BUG_ON(ti->preempt_count || !irqs_disabled()); 再次检查此函数是否被正确调用。 3189 3190 need_resched: 3191 add_preempt_count(PREEMPT_ACTIVE); 将抢占计数器加上一个数，禁止抢占再次发生。 3192 /* 3193 * We keep the big kernel semaphore locked, but we 3194 * clear ->lock_depth so that schedule() doesnt 3195 * auto-release the semaphore: 3196 */ 3197 #ifdef CONFIG_PREEMPT_BKL 3198 saved_lock_depth = task->lock_depth; 3199 task->lock_depth = -1; 3200 #endif 3201 local_irq_enable(); 因为我们是关闭了中断走到这里的，所以，运行调度程序之前，需要先打开中断。 3202 schedule(); 等本进程再次被调度执行的时候，仍然需要禁止中断。 3203 local_irq_disable(); 3204 #ifdef CONFIG_PREEMPT_BKL 3205 task->lock_depth = saved_lock_depth; 3206 #endif 3207 sub_preempt_count(PREEMPT_ACTIVE); 与前面的抢占计数器的加法相呼应。 3208 3209 /* we could miss a preemption opportunity between schedule and now */ 3210 barrier(); 3211 if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) 3212 goto need_resched; 3213 } 如果这个进程再次需要被调度，那么重新调度，不过如果真是这样，那么这个进程真是点被极了，只开了中断那么一小会就被抢占了。按上面来看，只是barrier一个语句；） 3214 3215 #endif /* CONFIG_PREEMPT */ |
| 153 void __lockfunc _spin_lock(spinlock_t *lock) 154 { 155 preempt_disable(); 156 _raw_spin_lock(lock); 157 } |
| 260 void __lockfunc _spin_unlock(spinlock_t *lock) 261 { 262 _raw_spin_unlock(lock); 263 preempt_enable(); 264 } |
| 63 # define might_resched() cond_resched() 64 #else 65 # define might_resched() do { } while (0) 66 #endif 67 68 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP 69 void __might_sleep(char *file, int line); 70 # define might_sleep() \ 71 do { __might_sleep(__FILE__, __LINE__); might_resched(); } while (0) 72 #else 73 # define might_sleep() do { might_resched(); } while (0) 74 #endif |
| 4086 static inline void __cond_resched(void) 4087 { 4088 /* 4089 * The BKS might be reacquired before we have dropped 4090 * PREEMPT_ACTIVE, which could trigger a second 4091 * cond_resched() call. 4092 */ 4093 if (unlikely(preempt_count())) 4094 return; 4095 do { 4096 add_preempt_count(PREEMPT_ACTIVE); 4097 schedule(); 4098 sub_preempt_count(PREEMPT_ACTIVE); 4099 } while (need_resched()); 4100 } 4101 4102 int __sched cond_resched(void) 4103 { 4104 if (need_resched()) { 4105 __cond_resched(); 4106 return 1; 4107 } 4108 return 0; 4109 } |
| 1 34 arch/i386/lib/usercopy.c <<__do_strncpy_from_user>> might_sleep(); \ 2 124 arch/i386/lib/usercopy.c <<__do_clear_user>> might_sleep(); \ 3 156 arch/i386/lib/usercopy.c < might_sleep(); 4 198 arch/i386/lib/usercopy.c < might_sleep(); 5 607 arch/i386/lib/usercopy.c < might_sleep(); 6 634 arch/i386/lib/usercopy.c < might_sleep(); 7 6 arch/i386/mm/highmem.c < might_sleep(); 8 2838 block/ll_rw_blk.c < might_sleep(); 9 1943 drivers/char/vt.c < might_sleep(); 10 2871 drivers/char/vt.c < might_sleep(); 11 2939 drivers/char/vt.c < might_sleep(); 12 693 drivers/infiniband/hw/mthca/mthca_cq.c < might_sleep(); 13 824 drivers/infiniband/hw/mthca/mthca_cq.c < might_sleep(); 14 343 drivers/infiniband/hw/mthca/mthca_mr.c < might_sleep(); 15 470 drivers/infiniband/hw/mthca/mthca_mr.c < might_sleep(); 16 498 drivers/infiniband/hw/mthca/mthca_mr.c < might_sleep(); 17 46 drivers/infiniband/hw/mthca/mthca_pd.c < might_sleep(); 18 69 drivers/infiniband/hw/mthca/mthca_pd.c < might_sleep(); 19 1420 drivers/usb/core/hcd.c < might_sleep (); 20 1468 fs/buffer.c <<__getblk>> might_sleep(); 21 1706 fs/buffer.c < might_sleep(); 22 153 fs/dcache.c < might_sleep(); 23 71 fs/ext3/inode.c < might_sleep(); 24 2951 fs/ext3/inode.c < might_sleep(); 25 135 fs/file_table.c <<__fput>> might_sleep(); 26 417 fs/fs-writeback.c < might_sleep(); 27 567 fs/fs-writeback.c < might_sleep(); 28 248 fs/inode.c < might_sleep(); 29 336 fs/jbd/revoke.c < might_sleep(); 30 982 fs/locks.c < might_sleep (); 31 1460 fs/locks.c < might_sleep(); 32 2545 fs/nfs/nfs4proc.c < might_sleep(); 33 2567 fs/nfs/nfs4proc.c < might_sleep(); 34 751 fs/nfs/nfs4state.c < might_sleep(); 35 589 fs/nfs/write.c < might_sleep(); 36 1944 fs/proc/base.c < might_sleep(); 37 51 include/asm-i386/checksum.h < might_sleep(); 38 184 include/asm-i386/checksum.h < might_sleep(); 39 99 include/asm-i386/semaphore.h < might_sleep(); 40 123 include/asm-i386/semaphore.h < might_sleep(); 41 438 include/asm-i386/uaccess.h <<__copy_to_user>> might_sleep(); 42 483 include/asm-i386/uaccess.h <<__copy_from_user>> might_sleep(); 43 76 include/linux/kernel.h < #define 6 #define might_sleep_if(cond...ely(cond)) might_sleep(); } while (0) 44 202 mm/mmap.c < might_sleep(); 45 85 mm/rmap.c < might_sleep(); |
