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SubjectRe: [RFC][PATCH 3/7] lockdep: Annotate read/write states
On Sun, Apr 17, 2011 at 11:45:08AM +0200, Peter Zijlstra wrote:
> From: Gautham R Shenoy <ego@in.ibm.com>
>
> Currently we do not save the recursive read dependencies in the dependency
> chain. As a result, a deadlock caused by the following chains are not spotted,
> since we never have the chain 1 in our dependency list:
>
> 1: Rlock(A) --> lock(B)
> 2: lock(B) --> Wlock(A), where A is a recursive read lock.
>
> Before adding the Recursive Read locks to the dependency chains, we need to
> distinguish them from the normal read locks since the conflicting states for
> these two are quite different.
>
> Currently the read/write status of a lock while it's acquired is denoted by a
> monotonically increasing variable where:
>
> 0 - WRITE
> 1 - READ
> 2 - RECURSIVE READ
>
> In this patch, we propose to modify this distinction from a monotonically
> increasing variable to a bit mask where:
>
> 0x1 - WRITE
> 0x2 - READ
> 0x4 - RECURSIVE READ
>
> This helps us to define the conflicting states for each lock with ease:
> Thereby, the conflicting states for a given states are defined as follows:
>
> Conflicting_states(WRITE): RECURSIVE_READ | READ | WRITE
> Conflicting_states(READ): READ | WRITE
> Conflicting_states(RECURSIVE_READ): WRITE
>
> Also, we use one more bit in the bitmask to distinguish the first recursive
> read in the current chain from the others, since it is sufficient to add only
> this dependency to the dependency list.
>
> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> include/linux/lockdep.h | 107 ++++++++++++++++++++++++++++++++++++------------
> kernel/lockdep.c | 46 ++++++++++----------
> 2 files changed, 105 insertions(+), 48 deletions(-)
>
> @@ -2273,7 +2273,7 @@ mark_held_locks(struct task_struct *curr
> hlock = curr->held_locks + i;
>
> usage_bit = 2 + (mark << 2); /* ENABLED */
> - if (hlock->read)
> + if (hlock->rw_state)

is_read(hlock->rw_state) ?



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