mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-03 00:46:40 +07:00
c598a070bc
Adds a lockdep.txt file and updates checklist.txt and whatisRCU.txt to reflect the new lockdep-enabled capabilities of RCU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-13-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
68 lines
2.6 KiB
Plaintext
68 lines
2.6 KiB
Plaintext
RCU and lockdep checking
|
|
|
|
All flavors of RCU have lockdep checking available, so that lockdep is
|
|
aware of when each task enters and leaves any flavor of RCU read-side
|
|
critical section. Each flavor of RCU is tracked separately (but note
|
|
that this is not the case in 2.6.32 and earlier). This allows lockdep's
|
|
tracking to include RCU state, which can sometimes help when debugging
|
|
deadlocks and the like.
|
|
|
|
In addition, RCU provides the following primitives that check lockdep's
|
|
state:
|
|
|
|
rcu_read_lock_held() for normal RCU.
|
|
rcu_read_lock_bh_held() for RCU-bh.
|
|
rcu_read_lock_sched_held() for RCU-sched.
|
|
srcu_read_lock_held() for SRCU.
|
|
|
|
These functions are conservative, and will therefore return 1 if they
|
|
aren't certain (for example, if CONFIG_DEBUG_LOCK_ALLOC is not set).
|
|
This prevents things like WARN_ON(!rcu_read_lock_held()) from giving false
|
|
positives when lockdep is disabled.
|
|
|
|
In addition, a separate kernel config parameter CONFIG_PROVE_RCU enables
|
|
checking of rcu_dereference() primitives:
|
|
|
|
rcu_dereference(p):
|
|
Check for RCU read-side critical section.
|
|
rcu_dereference_bh(p):
|
|
Check for RCU-bh read-side critical section.
|
|
rcu_dereference_sched(p):
|
|
Check for RCU-sched read-side critical section.
|
|
srcu_dereference(p, sp):
|
|
Check for SRCU read-side critical section.
|
|
rcu_dereference_check(p, c):
|
|
Use explicit check expression "c".
|
|
rcu_dereference_raw(p)
|
|
Don't check. (Use sparingly, if at all.)
|
|
|
|
The rcu_dereference_check() check expression can be any boolean
|
|
expression, but would normally include one of the rcu_read_lock_held()
|
|
family of functions and a lockdep expression. However, any boolean
|
|
expression can be used. For a moderately ornate example, consider
|
|
the following:
|
|
|
|
file = rcu_dereference_check(fdt->fd[fd],
|
|
rcu_read_lock_held() ||
|
|
lockdep_is_held(&files->file_lock) ||
|
|
atomic_read(&files->count) == 1);
|
|
|
|
This expression picks up the pointer "fdt->fd[fd]" in an RCU-safe manner,
|
|
and, if CONFIG_PROVE_RCU is configured, verifies that this expression
|
|
is used in:
|
|
|
|
1. An RCU read-side critical section, or
|
|
2. with files->file_lock held, or
|
|
3. on an unshared files_struct.
|
|
|
|
In case (1), the pointer is picked up in an RCU-safe manner for vanilla
|
|
RCU read-side critical sections, in case (2) the ->file_lock prevents
|
|
any change from taking place, and finally, in case (3) the current task
|
|
is the only task accessing the file_struct, again preventing any change
|
|
from taking place.
|
|
|
|
There are currently only "universal" versions of the rcu_assign_pointer()
|
|
and RCU list-/tree-traversal primitives, which do not (yet) check for
|
|
being in an RCU read-side critical section. In the future, separate
|
|
versions of these primitives might be created.
|