mywiki:linux:linux_kernel_notes
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Table of Minimum Spin Lock Requirements
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 |
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