Re: [PATCH v2] locking/lockdep: Revise Documentation/locking/crossrelease.txt
On 11/10/2017 4:30 PM, Ingo Molnar wrote: * Byungchul Park wrote: Event C depends on event A. Event A depends on event B. Event B depends on event C. - NOTE: Precisely speaking, a dependency is one between whether a - waiter for an event can be woken up and whether another waiter for - another event can be woken up. However from now on, we will describe - a dependency as if it's one between an event and another event for - simplicity. Why was this explanation removed? -Lockdep tries to detect a deadlock by checking dependencies created by -lock operations, acquire and release. Waiting for a lock corresponds to -waiting for an event, and releasing a lock corresponds to triggering an -event in the previous section. +Lockdep tries to detect a deadlock by checking circular dependencies +created by lock operations, acquire and release, which are wait and +event respectively. What? You changed a readable paragraph into an unreadable one. Sorry, this text needs to be acked by someone with good English skills, and I don't have the time right now to fix it all up. Please send minimal, obvious typo/grammar fixes only. I will send one including minimal fixes at the next spin. -- Thanks, Byungchul
Re: [PATCH v2] locking/lockdep: Revise Documentation/locking/crossrelease.txt
* Byungchul Park wrote: > Event C depends on event A. > Event A depends on event B. > Event B depends on event C. > > - NOTE: Precisely speaking, a dependency is one between whether a > - waiter for an event can be woken up and whether another waiter for > - another event can be woken up. However from now on, we will describe > - a dependency as if it's one between an event and another event for > - simplicity. Why was this explanation removed? > -Lockdep tries to detect a deadlock by checking dependencies created by > -lock operations, acquire and release. Waiting for a lock corresponds to > -waiting for an event, and releasing a lock corresponds to triggering an > -event in the previous section. > +Lockdep tries to detect a deadlock by checking circular dependencies > +created by lock operations, acquire and release, which are wait and > +event respectively. What? You changed a readable paragraph into an unreadable one. Sorry, this text needs to be acked by someone with good English skills, and I don't have the time right now to fix it all up. Please send minimal, obvious typo/grammar fixes only. Thanks, Ingo
Re: [PATCH v2] locking/lockdep: Revise Documentation/locking/crossrelease.txt
On Thu, Nov 09, 2017 at 04:20:36PM +0900, Byungchul Park wrote: > Changes from v1 > - Run several tools checking english spell and grammar over the text. > - Simplify the document more. Checker tools also reported other words e.g. crosslock, crossrelease, lockdep, mutex, lockless, and so on, but I left them unchanged since I thought it's better to leave it. Please let me know if I was wrong. Thanks, Byungchul > -8<- > >From 412bc9eb0d22791f70f7364bda189feb41899ff9 Mon Sep 17 00:00:00 2001 > From: Byungchul Park > Date: Thu, 9 Nov 2017 16:12:23 +0900 > Subject: [PATCH v2] locking/lockdep: Revise > Documentation/locking/crossrelease.txt > > Revise Documentation/locking/crossrelease.txt to enhance its readability. > > Signed-off-by: Byungchul Park > --- > Documentation/locking/crossrelease.txt | 492 > +++-- > 1 file changed, 227 insertions(+), 265 deletions(-) > > diff --git a/Documentation/locking/crossrelease.txt > b/Documentation/locking/crossrelease.txt > index bdf1423..11e3e3b 100644 > --- a/Documentation/locking/crossrelease.txt > +++ b/Documentation/locking/crossrelease.txt > @@ -12,10 +12,10 @@ Contents: > > (*) Limitation > > - - Limit lockdep > + - Limiting lockdep > - Pros from the limitation > - Cons from the limitation > - - Relax the limitation > + - Relaxing the limitation > > (*) Crossrelease > > @@ -30,9 +30,9 @@ Contents: > (*) Optimizations > > - Avoid duplication > - - Lockless for hot paths > + - Make hot paths lockless > > - (*) APPENDIX A: What lockdep does to work aggresively > + (*) APPENDIX A: How to add dependencies aggressively > > (*) APPENDIX B: How to avoid adding false dependencies > > @@ -51,36 +51,30 @@ also impossible due to the same reason. > > For example: > > - A context going to trigger event C is waiting for event A to happen. > - A context going to trigger event A is waiting for event B to happen. > - A context going to trigger event B is waiting for event C to happen. > + A context going to trigger event C is waiting for event A. > + A context going to trigger event A is waiting for event B. > + A context going to trigger event B is waiting for event C. > > -A deadlock occurs when these three wait operations run at the same time, > -because event C cannot be triggered if event A does not happen, which in > -turn cannot be triggered if event B does not happen, which in turn > -cannot be triggered if event C does not happen. After all, no event can > -be triggered since any of them never meets its condition to wake up. > +A deadlock occurs when the three waiters run at the same time, because > +event C cannot be triggered if event A does not happen, which in turn > +cannot be triggered if event B does not happen, which in turn cannot be > +triggered if event C does not happen. After all, no event can be > +triggered since any of them never meets its condition to wake up. > > -A dependency might exist between two waiters and a deadlock might happen > -due to an incorrect releationship between dependencies. Thus, we must > -define what a dependency is first. A dependency exists between them if: > +A dependency exists between two waiters, and a deadlock happens due to > +an incorrect relationship between dependencies. Thus, we must define > +what a dependency is first. A dependency exists between waiters if: > > 1. There are two waiters waiting for each event at a given time. > 2. The only way to wake up each waiter is to trigger its event. > 3. Whether one can be woken up depends on whether the other can. > > -Each wait in the example creates its dependency like: > +Each waiter in the example creates its dependency like: > > Event C depends on event A. > Event A depends on event B. > Event B depends on event C. > > - NOTE: Precisely speaking, a dependency is one between whether a > - waiter for an event can be woken up and whether another waiter for > - another event can be woken up. However from now on, we will describe > - a dependency as if it's one between an event and another event for > - simplicity. > - > And they form circular dependencies like: > > -> C -> A -> B - > @@ -101,19 +95,18 @@ Circular dependencies cause a deadlock. > How lockdep works > - > > -Lockdep tries to detect a deadlock by checking dependencies created by > -lock operations, acquire and release. Waiting for a lock corresponds to > -waiting for an event, and releasing a lock corresponds to triggering an > -event in the previous section. > +Lockdep tries
[PATCH v2] locking/lockdep: Revise Documentation/locking/crossrelease.txt
Changes from v1 - Run several tools checking english spell and grammar over the text. - Simplify the document more. -8<- >From 412bc9eb0d22791f70f7364bda189feb41899ff9 Mon Sep 17 00:00:00 2001 From: Byungchul Park Date: Thu, 9 Nov 2017 16:12:23 +0900 Subject: [PATCH v2] locking/lockdep: Revise Documentation/locking/crossrelease.txt Revise Documentation/locking/crossrelease.txt to enhance its readability. Signed-off-by: Byungchul Park --- Documentation/locking/crossrelease.txt | 492 +++-- 1 file changed, 227 insertions(+), 265 deletions(-) diff --git a/Documentation/locking/crossrelease.txt b/Documentation/locking/crossrelease.txt index bdf1423..11e3e3b 100644 --- a/Documentation/locking/crossrelease.txt +++ b/Documentation/locking/crossrelease.txt @@ -12,10 +12,10 @@ Contents: (*) Limitation - - Limit lockdep + - Limiting lockdep - Pros from the limitation - Cons from the limitation - - Relax the limitation + - Relaxing the limitation (*) Crossrelease @@ -30,9 +30,9 @@ Contents: (*) Optimizations - Avoid duplication - - Lockless for hot paths + - Make hot paths lockless - (*) APPENDIX A: What lockdep does to work aggresively + (*) APPENDIX A: How to add dependencies aggressively (*) APPENDIX B: How to avoid adding false dependencies @@ -51,36 +51,30 @@ also impossible due to the same reason. For example: - A context going to trigger event C is waiting for event A to happen. - A context going to trigger event A is waiting for event B to happen. - A context going to trigger event B is waiting for event C to happen. + A context going to trigger event C is waiting for event A. + A context going to trigger event A is waiting for event B. + A context going to trigger event B is waiting for event C. -A deadlock occurs when these three wait operations run at the same time, -because event C cannot be triggered if event A does not happen, which in -turn cannot be triggered if event B does not happen, which in turn -cannot be triggered if event C does not happen. After all, no event can -be triggered since any of them never meets its condition to wake up. +A deadlock occurs when the three waiters run at the same time, because +event C cannot be triggered if event A does not happen, which in turn +cannot be triggered if event B does not happen, which in turn cannot be +triggered if event C does not happen. After all, no event can be +triggered since any of them never meets its condition to wake up. -A dependency might exist between two waiters and a deadlock might happen -due to an incorrect releationship between dependencies. Thus, we must -define what a dependency is first. A dependency exists between them if: +A dependency exists between two waiters, and a deadlock happens due to +an incorrect relationship between dependencies. Thus, we must define +what a dependency is first. A dependency exists between waiters if: 1. There are two waiters waiting for each event at a given time. 2. The only way to wake up each waiter is to trigger its event. 3. Whether one can be woken up depends on whether the other can. -Each wait in the example creates its dependency like: +Each waiter in the example creates its dependency like: Event C depends on event A. Event A depends on event B. Event B depends on event C. - NOTE: Precisely speaking, a dependency is one between whether a - waiter for an event can be woken up and whether another waiter for - another event can be woken up. However from now on, we will describe - a dependency as if it's one between an event and another event for - simplicity. - And they form circular dependencies like: -> C -> A -> B - @@ -101,19 +95,18 @@ Circular dependencies cause a deadlock. How lockdep works - -Lockdep tries to detect a deadlock by checking dependencies created by -lock operations, acquire and release. Waiting for a lock corresponds to -waiting for an event, and releasing a lock corresponds to triggering an -event in the previous section. +Lockdep tries to detect a deadlock by checking circular dependencies +created by lock operations, acquire and release, which are wait and +event respectively. In short, lockdep does: 1. Detect a new dependency. - 2. Add the dependency into a global graph. + 2. Add the dependency to a global graph. 3. Check if that makes dependencies circular. - 4. Report a deadlock or its possibility if so. + 4. Report the deadlock if so. -For example, consider a graph built by lockdep that looks like: +For example, the graph has been built like: A -> B - \ @@ -123,7 +116,7 @@ For example, consider a graph built by lockdep that looks like: where A, B,..., E are different lock classes. -Lockdep will add a dependency into the graph on detection of a new +Lockdep will add a dependency to the grap
