Linux Concurrency and race conditions

• multiple user-space processes
• SMP
• preempible kernel code
• device interrupts
• delayed code execution mechanism, such as workqueues, taksklets and timers.
• hot-pluugable

2. Semaphores

Semaphores are used for mutual exlusion. can be used  when slepps are a possibility.

==> Reader/Writer Semaphores

3. Spinlocks

Spinlocks may be used in code that cannot sleep. Performance is higher than semaphores when properly used.

• Any time kernel code holds a spinlock, preemption is disable on the relevant processor.
• Disable interrupts while spinlock is held.
• spinlock mus always be held for the minimum time possible.

==> Reader/Writer spinlocks

4. Alternatives to Locking

1) Lock free algorithms

circular buffer

2) Atomic variables

you should not count on an atomic_t holding more than 24 bits.

3) Bit Operations

4) seqlock

5) read-copy-update

ldd3-ch5