user/sven/linux.git/lib/spinlock_debug.c, branch v3.9.7

lib/spinlock_debug: avoid livelock in do_raw_spin_lock()

2012-10-05T18:04:57Z

The logic in do_raw_spin_lock() attempts to acquire a spinlock by invoking arch_spin_trylock() in a loop with a delay between each attempt. Now consider the following situation in a 2 CPU system: 1. CPU-0 continually acquires and releases a spinlock in a tight loop; it stays in this loop until some condition X is satisfied. X can only be satisfied by another CPU. 2. CPU-1 tries to acquire the same spinlock, in an attempt to satisfy the aforementioned condition X. However, it never sees the unlocked value of the lock because the debug spinlock code uses trylock instead of just lock; it checks at all the wrong moments - whenever CPU-0 has locked the lock. Now in the absence of debug spinlocks, the architecture specific spinlock code can correctly allow CPU-1 to wait in a "queue" (e.g., ticket spinlocks), ensuring that it acquires the lock at some point. However, with the debug spinlock code, livelock can easily occur due to the use of try_lock, which obviously cannot put the CPU in that "queue". This queueing mechanism is implemented in both x86 and ARM spinlock code. Note that the situation mentioned above is not hypothetical. A real problem was encountered where CPU-0 was running hrtimer_cancel with interrupts disabled, and CPU-1 was attempting to run the hrtimer that CPU-0 was trying to cancel. Address this by actually attempting arch_spin_lock once it is suspected that there is a spinlock lockup. If we're in a situation that is described above, the arch_spin_lock should succeed; otherwise other timeout mechanisms (e.g., watchdog) should alert the system of a lockup. Therefore, if there is a genuine system problem and the spinlock can't be acquired, the end result (irrespective of this change being present) is the same. If there is a livelock caused by the debug code, this change will allow the lock to be acquired, depending on the implementation of the lower level arch specific spinlock code. [akpm@linux-foundation.org: tweak comment] Signed-off-by: Vikram Mulukutla Cc: Thomas Gleixner Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

spinlock_debug: print offset in addition to symbol name

2012-07-31T00:25:16Z

If there are two spinlocks embedded in a structure that kallsyms knows about and one of the spinlocks locks up we will print the name of the containing structure instead of the address of the lock. This is quite bad, so let's use %pS instead of %ps so we get an offset in addition to the symbol so we can determine which particular lock is having problems. Signed-off-by: Stephen Boyd Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

spinlock: Indicate that a lockup is only suspected

2012-06-06T09:34:20Z

On an over-committed KVM system we got a: "BUG: spinlock lockup on CPU#2, swapper/2/0" message on the heavily contended virtio blk spinlock. While we might want to reconsider the locking of virtio-blk (lock is held while switching to the host) this patch tries to make the message clearer: the lockup is only suspected. Signed-off-by: Christian Borntraeger Cc: Rusty Russell Cc: Michael S. Tsirkin Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1338283124-7063-1-git-send-email-borntraeger@de.ibm.com Signed-off-by: Ingo Molnar

spinlock_debug: print kallsyms name for lock

2012-05-29T23:22:33Z

When a spinlock warning is printed we usually get BUG: spinlock bad magic on CPU#0, modprobe/111 lock: 0xdff09f38, .magic: 00000000, .owner: /0, .owner_cpu: 0 but it's nicer to print the symbol for the lock if we have it so that we can avoid 'grep dff09f38 /proc/kallsyms' to find out which lock it was. Use kallsyms to print the symbol name so we get something a bit easier to read BUG: spinlock bad magic on CPU#0, modprobe/112 lock: test_lock, .magic: 00000000, .owner: /-1, .owner_cpu: 0 If the lock is not in kallsyms %ps will fall back to printing the address directly. Signed-off-by: Stephen Boyd Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

lib: reduce the use of module.h wherever possible

2012-03-07T20:04:04Z

For files only using THIS_MODULE and/or EXPORT_SYMBOL, map them onto including export.h -- or if the file isn't even using those, then just delete the include. Fix up any implicit include dependencies that were being masked by module.h along the way. Signed-off-by: Paul Gortmaker

lib/spinlock_debug.c: print owner on spinlock lockup

2011-11-01T00:30:56Z

When SPIN_BUG_ON is triggered, the lock owner information is reported. But it is omitted when spinlock lockup is detected. This information is useful especially on the architectures which don't implement trigger_all_cpu_backtrace() that is called just after detecting lockup. So report it and also avoid message format duplication. Signed-off-by: Akinobu Mita Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

locking: Further name space cleanups

2009-12-14T22:55:33Z

The name space hierarchy for the internal lock functions is now a bit backwards. raw_spin* functions map to _spin* which use __spin*, while we would like to have _raw_spin* and __raw_spin*. _raw_spin* is already used by lock debugging, so rename those funtions to do_raw_spin* to free up the _raw_spin* name space. No functional change. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Acked-by: Ingo Molnar

locking: Implement new raw_spinlock

2009-12-14T22:55:32Z

Now that the raw_spin name space is freed up, we can implement raw_spinlock and the related functions which are used to annotate the locks which are not converted to sleeping spinlocks in preempt-rt. A side effect is that only such locks can be used with the low level lock fsunctions which circumvent lockdep. For !rt spin_* functions are mapped to the raw_spin* implementations. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Acked-by: Ingo Molnar

locking: Convert raw_rwlock functions to arch_rwlock

2009-12-14T22:55:32Z

Name space cleanup for rwlock functions. No functional change. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Acked-by: David S. Miller Acked-by: Ingo Molnar Cc: linux-arch@vger.kernel.org

locking: Convert raw_rwlock to arch_rwlock

2009-12-14T22:55:32Z

Not strictly necessary for -rt as -rt does not have non sleeping rwlocks, but it's odd to not have a consistent naming convention. No functional change. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Acked-by: David S. Miller Acked-by: Ingo Molnar Cc: linux-arch@vger.kernel.org