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++ locking
Documentation/kernel-hacking/locking.rst
- atomic operations
Documentation/atomic_t.txt
atomic_t atomic64_t and atomic_long_t
atomic_read(), atomic_set()
atomic[_fetch]_{add,sub,inc,dec}()
atomic[_fetch]_{and,or,xor,andnot}()
..
- mutex
waiter can sleep, not usable in tasklets/timer/irqs
- spinlock / rwlock
spin_lock # use if lock is shared in different tasklets / only in user context
spin_lock_bh / disables softirqs # use if lock is shared in user context and softirqs (tasklets/timer)
spin_lock_irqsave / disables irqs # use if lock is shared in user context and irq context
--> Use irqsave variant if you're unsure
--> Avoid holding spinlock for more than 5 lines of code and across any
function call (except accessors like :c:func:`readb()`).
============== ============= ============= ========= ========= ========= ========= ======= ======= ============== ==============
. 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 SLIS None
Softirq A SLI SLI SL
Softirq B SLI SLI SL SL
Tasklet A SLI SLI SL SL None
Tasklet B SLI SLI SL SL SL None
Timer A SLI SLI SL SL SL SL None
Timer B SLI SLI SL SL SL SL SL None
User Context A SLI SLI SLBH SLBH SLBH SLBH SLBH SLBH None
User Context B SLI SLI SLBH SLBH SLBH SLBH SLBH SLBH MLI None
============== ============= ============= ========= ========= ========= ========= ======= ======= ============== ==============
Table: Table of Locking Requirements
+--------+----------------------------+
| SLIS | spin_lock_irqsave |
+--------+----------------------------+
| SLI | spin_lock_irq |
+--------+----------------------------+
| SL | spin_lock |
+--------+----------------------------+
| SLBH | spin_lock_bh |
+--------+----------------------------+
| MLI | mutex_lock_interruptible |
+--------+----------------------------+
Table: Legend for Locking Requirements Table
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