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Message-ID: <20201021032721.GA1982@boqun-laptop.fareast.corp.microsoft.com>
Date: Wed, 21 Oct 2020 11:27:21 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Linux Doc Mailing List <linux-doc@...r.kernel.org>,
Jonathan Corbet <corbet@....net>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] docs: lockdep-design: fix some warning issues
On Wed, Oct 21, 2020 at 02:17:23PM +0200, Mauro Carvalho Chehab wrote:
> There are several warnings caused by a recent change
> 224ec489d3cd ("lockdep/Documention: Recursive read lock detection reasoning")
>
> Those are reported by htmldocs build:
>
> Documentation/locking/lockdep-design.rst:429: WARNING: Definition list ends without a blank line; unexpected unindent.
> Documentation/locking/lockdep-design.rst:452: WARNING: Block quote ends without a blank line; unexpected unindent.
> Documentation/locking/lockdep-design.rst:453: WARNING: Unexpected indentation.
> Documentation/locking/lockdep-design.rst:453: WARNING: Blank line required after table.
> Documentation/locking/lockdep-design.rst:454: WARNING: Block quote ends without a blank line; unexpected unindent.
> Documentation/locking/lockdep-design.rst:455: WARNING: Unexpected indentation.
> Documentation/locking/lockdep-design.rst:455: WARNING: Blank line required after table.
> Documentation/locking/lockdep-design.rst:456: WARNING: Block quote ends without a blank line; unexpected unindent.
> Documentation/locking/lockdep-design.rst:457: WARNING: Unexpected indentation.
> Documentation/locking/lockdep-design.rst:457: WARNING: Blank line required after table.
>
> Besides the reported issues, there are some missing blank
> lines that ended producing wrong html output, and some
> literals are not properly identified.
>
> Also, the symbols used at the irq enabled/disable table
> are not displayed as expected, as they're not literals.
> Also, on another table they're using a different notation.
>
> Fixes: 224ec489d3cd ("lockdep/Documention: Recursive read lock detection reasoning")
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Acked-by: Boqun Feng <boqun.feng@...il.com>
Regards,
Boqun
> ---
> Documentation/locking/lockdep-design.rst | 51 ++++++++++++++----------
> 1 file changed, 31 insertions(+), 20 deletions(-)
>
> diff --git a/Documentation/locking/lockdep-design.rst b/Documentation/locking/lockdep-design.rst
> index cec03bd1294a..9f3cfca9f8a4 100644
> --- a/Documentation/locking/lockdep-design.rst
> +++ b/Documentation/locking/lockdep-design.rst
> @@ -42,6 +42,7 @@ The validator tracks lock-class usage history and divides the usage into
> (4 usages * n STATEs + 1) categories:
>
> where the 4 usages can be:
> +
> - 'ever held in STATE context'
> - 'ever held as readlock in STATE context'
> - 'ever held with STATE enabled'
> @@ -49,10 +50,12 @@ where the 4 usages can be:
>
> where the n STATEs are coded in kernel/locking/lockdep_states.h and as of
> now they include:
> +
> - hardirq
> - softirq
>
> where the last 1 category is:
> +
> - 'ever used' [ == !unused ]
>
> When locking rules are violated, these usage bits are presented in the
> @@ -96,9 +99,9 @@ exact case is for the lock as of the reporting time.
> +--------------+-------------+--------------+
> | | irq enabled | irq disabled |
> +--------------+-------------+--------------+
> - | ever in irq | ? | - |
> + | ever in irq | '?' | '-' |
> +--------------+-------------+--------------+
> - | never in irq | + | . |
> + | never in irq | '+' | '.' |
> +--------------+-------------+--------------+
>
> The character '-' suggests irq is disabled because if otherwise the
> @@ -216,7 +219,7 @@ looks like this::
> BD_MUTEX_PARTITION
> };
>
> -mutex_lock_nested(&bdev->bd_contains->bd_mutex, BD_MUTEX_PARTITION);
> + mutex_lock_nested(&bdev->bd_contains->bd_mutex, BD_MUTEX_PARTITION);
>
> In this case the locking is done on a bdev object that is known to be a
> partition.
> @@ -334,7 +337,7 @@ Troubleshooting:
> ----------------
>
> The validator tracks a maximum of MAX_LOCKDEP_KEYS number of lock classes.
> -Exceeding this number will trigger the following lockdep warning:
> +Exceeding this number will trigger the following lockdep warning::
>
> (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
>
> @@ -420,7 +423,8 @@ the critical section of another reader of the same lock instance.
>
> The difference between recursive readers and non-recursive readers is because:
> recursive readers get blocked only by a write lock *holder*, while non-recursive
> -readers could get blocked by a write lock *waiter*. Considering the follow example:
> +readers could get blocked by a write lock *waiter*. Considering the follow
> +example::
>
> TASK A: TASK B:
>
> @@ -448,20 +452,22 @@ There are simply four block conditions:
>
> Block condition matrix, Y means the row blocks the column, and N means otherwise.
>
> - | E | r | R |
> +---+---+---+---+
> - E | Y | Y | Y |
> + | | E | r | R |
> +---+---+---+---+
> - r | Y | Y | N |
> + | E | Y | Y | Y |
> + +---+---+---+---+
> + | r | Y | Y | N |
> + +---+---+---+---+
> + | R | Y | Y | N |
> +---+---+---+---+
> - R | Y | Y | N |
>
> (W: writers, r: non-recursive readers, R: recursive readers)
>
>
> acquired recursively. Unlike non-recursive read locks, recursive read locks
> only get blocked by current write lock *holders* other than write lock
> -*waiters*, for example:
> +*waiters*, for example::
>
> TASK A: TASK B:
>
> @@ -491,7 +497,7 @@ Recursive locks don't block each other, while non-recursive locks do (this is
> even true for two non-recursive read locks). A non-recursive lock can block the
> corresponding recursive lock, and vice versa.
>
> -A deadlock case with recursive locks involved is as follow:
> +A deadlock case with recursive locks involved is as follow::
>
> TASK A: TASK B:
>
> @@ -510,7 +516,7 @@ because there are 3 types for lockers, there are, in theory, 9 types of lock
> dependencies, but we can show that 4 types of lock dependencies are enough for
> deadlock detection.
>
> -For each lock dependency:
> +For each lock dependency::
>
> L1 -> L2
>
> @@ -525,20 +531,25 @@ same types).
> With the above combination for simplification, there are 4 types of dependency edges
> in the lockdep graph:
>
> -1) -(ER)->: exclusive writer to recursive reader dependency, "X -(ER)-> Y" means
> +1) -(ER)->:
> + exclusive writer to recursive reader dependency, "X -(ER)-> Y" means
> X -> Y and X is a writer and Y is a recursive reader.
>
> -2) -(EN)->: exclusive writer to non-recursive locker dependency, "X -(EN)-> Y" means
> +2) -(EN)->:
> + exclusive writer to non-recursive locker dependency, "X -(EN)-> Y" means
> X -> Y and X is a writer and Y is either a writer or non-recursive reader.
>
> -3) -(SR)->: shared reader to recursive reader dependency, "X -(SR)-> Y" means
> +3) -(SR)->:
> + shared reader to recursive reader dependency, "X -(SR)-> Y" means
> X -> Y and X is a reader (recursive or not) and Y is a recursive reader.
>
> -4) -(SN)->: shared reader to non-recursive locker dependency, "X -(SN)-> Y" means
> +4) -(SN)->:
> + shared reader to non-recursive locker dependency, "X -(SN)-> Y" means
> X -> Y and X is a reader (recursive or not) and Y is either a writer or
> non-recursive reader.
>
> -Note that given two locks, they may have multiple dependencies between them, for example:
> +Note that given two locks, they may have multiple dependencies between them,
> +for example::
>
> TASK A:
>
> @@ -592,11 +603,11 @@ circles that won't cause deadlocks.
>
> Proof for sufficiency (Lemma 1):
>
> -Let's say we have a strong circle:
> +Let's say we have a strong circle::
>
> L1 -> L2 ... -> Ln -> L1
>
> -, which means we have dependencies:
> +, which means we have dependencies::
>
> L1 -> L2
> L2 -> L3
> @@ -633,7 +644,7 @@ a lock held by P2, and P2 is waiting for a lock held by P3, ... and Pn is waitin
> for a lock held by P1. Let's name the lock Px is waiting as Lx, so since P1 is waiting
> for L1 and holding Ln, so we will have Ln -> L1 in the dependency graph. Similarly,
> we have L1 -> L2, L2 -> L3, ..., Ln-1 -> Ln in the dependency graph, which means we
> -have a circle:
> +have a circle::
>
> Ln -> L1 -> L2 -> ... -> Ln
>
> --
> 2.26.2
>
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