linux-toradex.git/include/linux/rwbase_rt.h, branch v6.13-rc6 Linux kernel for Apalis and Colibri modules locking: Make rwsem_assert_held_write_nolockdep() build with PREEMPT_RT=y 2024-04-08T14:39:16+00:00 Sebastian Andrzej Siewior bigeasy@linutronix.de 2024-03-19T18:20:50+00:00 fa1f51162338b3e2f520d4bfedc42b3b2e00da6d The commit cited below broke the build for PREEMPT_RT because rwsem_assert_held_write_nolockdep() passes a struct rw_semaphore but rw_base_assert_held_write() expects struct rwbase_rt. Fixing the type alone leads to the problem that WARN_ON() is not found because bug.h is missing. In order to resolve this: - Keep the assert (WARN_ON()) in rwsem.h (not rwbase_rt.h) - Make rwsem_assert_held_write_nolockdep() do the implementation specific (rw_base) writer check. - Replace the "inline" with __always_inline which was used before. Fixes: f70405afc99b1 ("locking: Add rwsem_assert_held() and rwsem_assert_held_write()") Reported-by: Clark Williams <williams@redhat.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Waiman Long <longman@redhat.com> Link: https://lore.kernel.org/r/20240319182050.U4AzUF3I@linutronix.de 
The commit cited below broke the build for PREEMPT_RT because
rwsem_assert_held_write_nolockdep() passes a struct rw_semaphore but
rw_base_assert_held_write() expects struct rwbase_rt. Fixing the type alone
leads to the problem that WARN_ON() is not found because bug.h is missing.

In order to resolve this:

 - Keep the assert (WARN_ON()) in rwsem.h (not rwbase_rt.h)

 - Make rwsem_assert_held_write_nolockdep() do the implementation
   specific (rw_base) writer check.

 - Replace the "inline" with __always_inline which was used before.

Fixes: f70405afc99b1 ("locking: Add rwsem_assert_held() and rwsem_assert_held_write()")
Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20240319182050.U4AzUF3I@linutronix.de
locking: Add rwsem_assert_held() and rwsem_assert_held_write() 2024-02-19T15:49:33+00:00 Matthew Wilcox (Oracle) willy@infradead.org 2024-02-19T15:41:11+00:00 f70405afc99b1e5a3a1e60b6c05456fde2dbe622 Modelled after lockdep_assert_held() and lockdep_assert_held_write(), but are always active, even when lockdep is disabled. Of course, they don't test that _this_ thread is the owner, but it's sufficient to catch many bugs and doesn't incur the same performance penalty as lockdep. Acked-by: "Peter Zijlstra (Intel)" <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Acked-by: "Darrick J. Wong" <djwong@kernel.org> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org> Signed-off-by: Chandan Babu R <chandanbabu@kernel.org> 
Modelled after lockdep_assert_held() and lockdep_assert_held_write(),
but are always active, even when lockdep is disabled.  Of course, they
don't test that _this_ thread is the owner, but it's sufficient to catch
many bugs and doesn't incur the same performance penalty as lockdep.

Acked-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
locking/rt: Add base code for RT rw_semaphore and rwlock 2021-08-17T15:12:22+00:00 Thomas Gleixner tglx@linutronix.de 2021-08-15T21:28:03+00:00 943f0edb754fac195043c620b44f920e4fb76ec8 On PREEMPT_RT, rw_semaphores and rwlocks are substituted with an rtmutex and a reader count. The implementation is writer unfair, as it is not feasible to do priority inheritance on multiple readers, but experience has shown that real-time workloads are not the typical workloads which are sensitive to writer starvation. The inner workings of rw_semaphores and rwlocks on RT are almost identical except for the task state and signal handling. rw_semaphores are not state preserving over a contention, they are expected to enter and leave with state == TASK_RUNNING. rwlocks have a mechanism to preserve the state of the task at entry and restore it after unblocking taking potential non-lock related wakeups into account. rw_semaphores can also be subject to signal handling interrupting a blocked state, while rwlocks ignore signals. To avoid code duplication, provide a shared implementation which takes the small difference vs. state and signals into account. The code is included into the relevant rw_semaphore/rwlock base code and compiled for each use case separately. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210815211302.957920571@linutronix.de 
On PREEMPT_RT, rw_semaphores and rwlocks are substituted with an rtmutex and
a reader count. The implementation is writer unfair, as it is not feasible
to do priority inheritance on multiple readers, but experience has shown
that real-time workloads are not the typical workloads which are sensitive
to writer starvation.

The inner workings of rw_semaphores and rwlocks on RT are almost identical
except for the task state and signal handling. rw_semaphores are not state
preserving over a contention, they are expected to enter and leave with state
== TASK_RUNNING. rwlocks have a mechanism to preserve the state of the task
at entry and restore it after unblocking taking potential non-lock related
wakeups into account. rw_semaphores can also be subject to signal handling
interrupting a blocked state, while rwlocks ignore signals.

To avoid code duplication, provide a shared implementation which takes the
small difference vs. state and signals into account. The code is included
into the relevant rw_semaphore/rwlock base code and compiled for each use
case separately.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.957920571@linutronix.de