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Linux 5.3 compat: rw_semaphore owner

Browse Source 
Commit https://github.com/torvalds/linux/commit/94a9717b updated the
rwsem's owner field to contain additional flags describing the rwsem's
state.  Rather then update the wrappers to mask out these bits, the
code no longer relies on the owner stored by the kernel.  This does
increase the size of a krwlock_t but it makes the implementation
less sensitive to future kernel changes.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #9029
This commit is contained in:
Brian Behlendorf 2019-07-12 13:27:24 -07:00 committed by Tony Hutter
parent 4c98586daf
commit 54561073e7
2 changed files with 6 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
include/spl/sys/rwlock.h
View File

@ -78,15 +78,9 @@ typedef enum {
RW_READER = 2
} krw_t;
/*
* If CONFIG_RWSEM_SPIN_ON_OWNER is defined, rw_semaphore will have an owner
* field, so we don't need our own.
*/
typedef struct {
struct rw_semaphore rw_rwlock;
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
kthread_t *rw_owner;
#endif
#ifdef CONFIG_LOCKDEP
krw_type_t rw_type;
#endif /* CONFIG_LOCKDEP */
@ -97,31 +91,19 @@ typedef struct {
static inline void
spl_rw_set_owner(krwlock_t *rwp)
{
/*
* If CONFIG_RWSEM_SPIN_ON_OWNER is defined, down_write, up_write,
* downgrade_write and __init_rwsem will set/clear owner for us.
*/
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
rwp->rw_owner = current;
#endif
}
static inline void
spl_rw_clear_owner(krwlock_t *rwp)
{
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
rwp->rw_owner = NULL;
#endif
}
static inline kthread_t *
rw_owner(krwlock_t *rwp)
{
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
return (SEM(rwp)->owner);
#else
return (rwp->rw_owner);
#endif
}
#ifdef CONFIG_LOCKDEP
@ -148,6 +130,11 @@ spl_rw_lockdep_on_maybe(krwlock_t *rwp) \
#define spl_rw_lockdep_on_maybe(rwp)
#endif /* CONFIG_LOCKDEP */
static inline int
RW_LOCK_HELD(krwlock_t *rwp)
{
return (spl_rwsem_is_locked(SEM(rwp)));
}
static inline int
RW_WRITE_HELD(krwlock_t *rwp)
@ -155,55 +142,10 @@ RW_WRITE_HELD(krwlock_t *rwp)
return (rw_owner(rwp) == current);
}
static inline int
RW_LOCK_HELD(krwlock_t *rwp)
{
return (spl_rwsem_is_locked(SEM(rwp)));
}
static inline int
RW_READ_HELD(krwlock_t *rwp)
{
if (!RW_LOCK_HELD(rwp))
return (0);
/*
* rw_semaphore cheat sheet:
*
* < 3.16:
* There's no rw_semaphore.owner, so use rwp.owner instead.
* If rwp.owner == NULL then it's a reader
*
* 3.16 - 4.7:
* rw_semaphore.owner added (https://lwn.net/Articles/596656/)
* and CONFIG_RWSEM_SPIN_ON_OWNER introduced.
* If rw_semaphore.owner == NULL then it's a reader
*
* 4.8 - 4.16.16:
* RWSEM_READER_OWNED added as an internal #define.
* (https://lore.kernel.org/patchwork/patch/678590/)
* If rw_semaphore.owner == 1 then it's a reader
*
* 4.16.17 - 4.19:
* RWSEM_OWNER_UNKNOWN introduced as ((struct task_struct *)-1L)
* (https://do-db2.lkml.org/lkml/2018/5/15/985)
* If rw_semaphore.owner == 1 then it's a reader.
*
* 4.20+:
* RWSEM_OWNER_UNKNOWN changed to ((struct task_struct *)-2L)
* (https://lkml.org/lkml/2018/9/6/986)
* If rw_semaphore.owner & 1 then it's a reader, and also the reader's
* task_struct may be embedded in rw_semaphore->owner.
*/
#if defined(CONFIG_RWSEM_SPIN_ON_OWNER) && defined(RWSEM_OWNER_UNKNOWN)
if (RWSEM_OWNER_UNKNOWN == (struct task_struct *)-2L) {
/* 4.20+ kernels with CONFIG_RWSEM_SPIN_ON_OWNER */
return ((unsigned long) SEM(rwp)->owner & 1);
}
#endif
/* < 4.20 kernel or !CONFIG_RWSEM_SPIN_ON_OWNER */
return (rw_owner(rwp) == NULL || (unsigned long) rw_owner(rwp) == 1);
return (RW_LOCK_HELD(rwp) && rw_owner(rwp) == NULL);
}
/*

3
module/spl/spl-rwlock.c
View File

@ -119,9 +119,6 @@ rwsem_tryupgrade(struct rw_semaphore *rwsem)
if (__rwsem_tryupgrade(rwsem)) {
rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
rwsem->owner = current;
#endif
return (1);
}
return (0);