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--- mywiki:linux:linux_kernel_notes [2015/04/02 15:10] – shaoguoh
+++ mywiki:linux:linux_kernel_notes [2019/09/15 18:55] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
-Table of Minimum Spin Lock Requirements
+| [[http://www.linux-mips.org/wiki/Linux/MIPS_Porting_Guide|MIPS Porting Guide]] |
+===== Kernel Context knowledge =====
+| process context | includes user context, kernel thread, work queue |
+| User Context | The kernel executing on behalf of a particular process (ie. a system call or trap, ioctl, module_init, module_exit or kernel thread, workqueue. You can tell which process with the current macro.) Not to be confused with userspace. Can be interrupted by software or hardware interrupts. |
+| Userspace (not kernel) | A process executing its own code outside the kernel |
+| Interrupt context | includes hard irq, kernel timer, softirq, tasklet | if in_interrupt() true |
+| Hardware IRQ | Hardware interrupt request | if in_irq() true |
+| Softirq | Software interrupt handler. in_irq() returns false; in_softirq() returns true. Tasklets and softirqs both fall into the category of 'software interrupts'. Strictly speaking a softirq is one of up to 32 enumerated software interrupts which can run on multiple CPUs at once. Sometimes used to refer to tasklets as well (ie. all software interrupts). | if in_irq() false and in_softirq() true |
+| Tasklet | A dynamically-registered software interrupt, which is guaranteed to only run on one CPU at a time |
+| Timer | which is running at (or close to) a given time. When running, it is just like a tasklet (in fact, they are called from the TIMER_SOFTIRQ). |
-The following table lists the minimum locking requirements between various contexts. In some cases, the same context can only be running on one CPU at a time, so no locking is required for that context (eg. a particular thread can only run on one CPU at a time, but if it needs shares data with another thread, locking is required).
-Remember the advice above: you can always use spin_lock_irqsave(), which is a superset of all other spinlock primitives.
-|  | IRQ Handler A | IRQ Handler B | Softirq A | Softirq B | Tasklet A | Tasklet B | Timer A | Timer B | User Context A | User Context B |
-| IRQ Handler A | None |
-| IRQ Handler B | spin_lock_irqsave() | None |
-| Softirq A | spin_lock_irq() | spin_lock_irq() | spin_lock() |
-| Softirq B | spin_lock_irq() | spin_lock_irq() | spin_lock() | spin_lock() |
-| Tasklet A | spin_lock_irq() | spin_lock_irq() | spin_lock() | spin_lock() | None |
-| Tasklet B | spin_lock_irq() | spin_lock_irq() | spin_lock() | spin_lock() | spin_lock() | None |
-| Timer A | spin_lock_irq() | spin_lock_irq() | spin_lock() | spin_lock() | spin_lock() | spin_lock() | None |
-| Timer B | spin_lock_irq() | spin_lock_irq() | spin_lock() | spin_lock() | spin_lock() | spin_lock() | spin_lock() | None |
-| User Context | A spin_lock_irq() | spin_lock_irq() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | None |
-| User Context B | spin_lock_irq() | spin_lock_irq() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | spin_lock_bh() | down_interruptible | None |