On Sat, Dec 06, 2025 at 07:25:22AM +0700, Bagas Sanjaya wrote: > On Fri, Dec 05, 2025 at 04:18:38PM +0900, Byungchul Park wrote: > > Add documents describing the concept and APIs of dept. > > > > Signed-off-by: Byungchul Park <[email protected]> > > --- > > Documentation/dev-tools/dept.rst | 778 +++++++++++++++++++++++++++ > > Documentation/dev-tools/dept_api.rst | 125 +++++ > > You forget to add toctree entries:
I'm sorry for late reply. Thanks a lot! > ---- >8 ---- > diff --git a/Documentation/dev-tools/index.rst > b/Documentation/dev-tools/index.rst > index 4b8425e348abd1..02c858f5ed1fa2 100644 > --- a/Documentation/dev-tools/index.rst > +++ b/Documentation/dev-tools/index.rst > @@ -22,6 +22,8 @@ Documentation/process/debugging/index.rst > clang-format > coccinelle > sparse > + dept > + dept_api > kcov > gcov > kasan > > > +Lockdep detects a deadlock by checking lock acquisition order. For > > +example, a graph to track acquisition order built by lockdep might look > > +like: > > + > > +.. literal:: > > + > > + A -> B - > > + \ > > + -> E > > + / > > + C -> D - > > + > > + where 'A -> B' means that acquisition A is prior to acquisition B > > + with A still held. > > Use code-block directive for literal code blocks: I will. > ---- >8 ---- > diff --git a/Documentation/dev-tools/dept.rst > b/Documentation/dev-tools/dept.rst > index 333166464543d7..8394c4ea81bc2a 100644 > --- a/Documentation/dev-tools/dept.rst > +++ b/Documentation/dev-tools/dept.rst > @@ -10,7 +10,7 @@ Lockdep detects a deadlock by checking lock acquisition > order. For > example, a graph to track acquisition order built by lockdep might look > like: > > -.. literal:: > +.. code-block:: > > A -> B - > \ > @@ -25,7 +25,7 @@ Lockdep keeps adding each new acquisition order into the > graph at > runtime. For example, 'E -> C' will be added when the two locks have > been acquired in the order, E and then C. The graph will look like: > > -.. literal:: > +.. code-block:: > > A -> B - > \ > @@ -41,7 +41,7 @@ been acquired in the order, E and then C. The graph will > look like: > > This graph contains a subgraph that demonstrates a loop like: > > -.. literal:: > +.. code-block:: > > -> E - > / \ > @@ -76,7 +76,7 @@ e.g. irq context, normal process context, wq worker > context, or so on. > > Can lockdep detect the following deadlock? > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -91,7 +91,7 @@ Can lockdep detect the following deadlock? > > No. What about the following? > > -.. literal:: > +.. code-block:: > > context X context Y > > @@ -116,7 +116,7 @@ What leads a deadlock > A deadlock occurs when one or multi contexts are waiting for events that > will never happen. For example: > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -148,7 +148,7 @@ In terms of dependency: > > Dependency graph reflecting this example will look like: > > -.. literal:: > +.. code-block:: > > -> C -> A -> B - > / \ > @@ -171,7 +171,7 @@ Introduce DEPT > DEPT(DEPendency Tracker) tracks wait and event instead of lock > acquisition order so as to recognize the following situation: > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -186,7 +186,7 @@ acquisition order so as to recognize the following > situation: > and builds up a dependency graph at runtime that is similar to lockdep. > The graph might look like: > > -.. literal:: > +.. code-block:: > > -> C -> A -> B - > / \ > @@ -199,7 +199,7 @@ DEPT keeps adding each new dependency into the graph at > runtime. For > example, 'B -> D' will be added when event D occurrence is a > prerequisite to reaching event B like: > > -.. literal:: > +.. code-block:: > > context W > > @@ -211,7 +211,7 @@ prerequisite to reaching event B like: > > After the addition, the graph will look like: > > -.. literal:: > +.. code-block:: > > -> D > / > @@ -236,7 +236,7 @@ How DEPT works > Let's take a look how DEPT works with the 1st example in the section > 'Limitation of lockdep'. > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -256,7 +256,7 @@ event. > > Adding comments to describe DEPT's view in detail: > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -293,7 +293,7 @@ Adding comments to describe DEPT's view in detail: > > Let's build up dependency graph with this example. Firstly, context X: > > -.. literal:: > +.. code-block:: > > context X > > @@ -304,7 +304,7 @@ Let's build up dependency graph with this example. > Firstly, context X: > > There are no events to create dependency. Next, context Y: > > -.. literal:: > +.. code-block:: > > context Y > > @@ -332,7 +332,7 @@ event A cannot be triggered if wait B cannot be awakened > by event B. > Therefore, we can say event A depends on event B, say, 'A -> B'. The > graph will look like after adding the dependency: > > -.. literal:: > +.. code-block:: > > A -> B > > @@ -340,7 +340,7 @@ graph will look like after adding the dependency: > > Lastly, context Z: > > -.. literal:: > +.. code-block:: > > context Z > > @@ -362,7 +362,7 @@ triggered if wait A cannot be awakened by event A. > Therefore, we can > say event B depends on event A, say, 'B -> A'. The graph will look like > after adding the dependency: > > -.. literal:: > +.. code-block:: > > -> A -> B - > / \ > @@ -386,7 +386,7 @@ Interpret DEPT report > > The following is the same example in the section 'How DEPT works'. > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -425,7 +425,7 @@ We can simplify this by labeling each waiting point with > [W], each > point where its event's context starts with [S] and each event with [E]. > This example will look like after the labeling: > > -.. literal:: > +.. code-block:: > > context X context Y context Z > > @@ -443,7 +443,7 @@ DEPT uses the symbols [W], [S] and [E] in its report as > described above. > The following is an example reported by DEPT for a real problem in > practice. > > -.. literal:: > +.. code-block:: > > Link: > https://lore.kernel.org/lkml/[email protected]/#t > Link: > https://lore.kernel.org/lkml/[email protected]/ > @@ -646,7 +646,7 @@ practice. > > Let's take a look at the summary that is the most important part. > > -.. literal:: > +.. code-block:: > > --------------------------------------------------- > summary > @@ -669,7 +669,7 @@ Let's take a look at the summary that is the most > important part. > > The summary shows the following scenario: > > -.. literal:: > +.. code-block:: > > context A context B context ?(unknown) > > @@ -684,7 +684,7 @@ The summary shows the following scenario: > > Adding comments to describe DEPT's view in detail: > > -.. literal:: > +.. code-block:: > > context A context B context ?(unknown) > > @@ -711,7 +711,7 @@ Adding comments to describe DEPT's view in detail: > > Let's build up dependency graph with this report. Firstly, context A: > > -.. literal:: > +.. code-block:: > > context A > > @@ -735,7 +735,7 @@ unlock(&ni->ni_lock:0) depends on folio_unlock(&f1), say, > > The graph will look like after adding the dependency: > > -.. literal:: > +.. code-block:: > > unlock(&ni->ni_lock:0) -> folio_unlock(&f1) > > @@ -743,7 +743,7 @@ The graph will look like after adding the dependency: > > Secondly, context B: > > -.. literal:: > +.. code-block:: > > context B > > @@ -762,7 +762,7 @@ folio_unlock(&f1) depends on unlock(&ni->ni_lock:0), say, > > The graph will look like after adding the dependency: > > -.. literal:: > +.. code-block:: > > -> unlock(&ni->ni_lock:0) -> folio_unlock(&f1) - > / \ > > > +Limitation of lockdep > > +--------------------- > > + > > +Lockdep deals with a deadlock by typical lock e.g. spinlock and mutex, > > +that are supposed to be released within the acquisition context. > > +However, when it comes to a deadlock by folio lock that is not supposed > > +to be released within the acquisition context or other general > > +synchronization mechanisms, lockdep doesn't work. > > + > > +NOTE: In this document, 'context' refers to any type of unique context > > +e.g. irq context, normal process context, wq worker context, or so on. > > + > > +Can lockdep detect the following deadlock? > > + > > +.. literal:: > > + > > + context X context Y context Z > > + > > + mutex_lock A > > + folio_lock B > > + folio_lock B <- DEADLOCK > > + mutex_lock A <- DEADLOCK > > + folio_unlock B > > + folio_unlock B > > + mutex_unlock A > > + mutex_unlock A > > + > > +No. What about the following? > > + > > +.. literal:: > > + > > + context X context Y > > + > > + mutex_lock A > > + mutex_lock A <- DEADLOCK > > + wait_for_complete B <- DEADLOCK > > + complete B > > + mutex_unlock A > > + mutex_unlock A > > + > > +No. > > One unanswered question from my v17 review [1]: You explain in "How DEPT > works" > section how DEPT detects deadlock in the first example (the former with three > contexts). Can you do the same on the second example (the latter with two > contexts)? Did you mean to update the document with it? I misunderstood what you meant but sure I will update it as [1]. [1] https://lore.kernel.org/linux-doc/[email protected]/ Thanks. Byungchul > Thanks. > > [1]: https://lore.kernel.org/linux-doc/[email protected]/ > > -- > An old man doll... just what I always wanted! - Clara
