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locking/percpu-rwsem: Remove the embedded rwsem

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The filesystem freezer uses percpu-rwsem in a way that is effectively
write_non_owner() and achieves this with a few horrible hacks that
rely on the rwsem (!percpu) implementation.

When PREEMPT_RT replaces the rwsem implementation with a PI aware
variant this comes apart.

Remove the embedded rwsem and implement it using a waitqueue and an
atomic_t.

 - make readers_block an atomic, and use it, with the waitqueue
   for a blocking test-and-set write-side.

 - have the read-side wait for the 'lock' state to clear.

Have the waiters use FIFO queueing and mark them (reader/writer) with
a new WQ_FLAG. Use a custom wake_function to wake either a single
writer or all readers until a writer.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200204092403.GB14879@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra
2019-10-30 20:30:41 +01:00
committed by Ingo Molnar
parent 75ff64572e
commit 7f26482a87
5 changed files with 126 additions and 74 deletions
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12
kernel/locking/rwsem.h
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@@ -1,12 +0,0 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __INTERNAL_RWSEM_H
#define __INTERNAL_RWSEM_H
#include <linux/rwsem.h>
extern void __down_read(struct rw_semaphore *sem);
extern void __up_read(struct rw_semaphore *sem);
extern void __down_write(struct rw_semaphore *sem);
extern void __up_write(struct rw_semaphore *sem);
#endif /* __INTERNAL_RWSEM_H */