Hi,
Andrew Doran <a...@netbsd.org> writes:
> Hi,
>
> This also happened the last time I touched rw_downgrade(), and I backed out
> the change then, but both times I don't see the bug. I have some questions:
>
> - Are you running DIAGNOSTIC and/or LOCKDEBUG? I would be very interested
> to see what happens with a LOCKDEBUG kernel here.
I will enable LOCKDEBUG and DIAGNOSTIC soon.
> - Do you have an ATI Radeon graphics chip?
> - Are you using ZFS?
My GPU is in Intel CPU (KabyLake Refresh).
And I do not use ZFS at all. All partitions are FFSv2 with WAPBL.
> Thanks,
> Andrew
>
>
> On Mon, Jan 20, 2020 at 12:41:37PM +0900, Ryo ONODERA wrote:
>> Hi,
>>
>> After this commit, the kernel stalls just before root file system
>> will be found on my NetBSD/amd64 laptop.
>>
>> Reverting
>> src/sys/kern/kern_rwlock.c to r1.60
>> and
>> src/sys/sys/rwlock.h to r1.12
>> in latest -current tree and I can get the kernel that works like
>> before.
>>
>> And on another laptop, the problematic kernel stalls before root file
>> system detection like my laptop.
>>
>> It may be universal problem.
>>
>> Could you take a look at this problem?
>>
>> Thank you.
>>
>> "Andrew Doran" <a...@netbsd.org> writes:
>>
>> > Module Name: src
>> > Committed By: ad
>> > Date: Sun Jan 19 18:34:24 UTC 2020
>> >
>> > Modified Files:
>> > src/sys/kern: kern_rwlock.c
>> > src/sys/sys: rwlock.h
>> >
>> > Log Message:
>> > Tidy rwlocks a bit, no functional change intended. Mainly:
>> >
>> > - rw_downgrade(): do it in a for () loop like all the others.
>> > - Explicitly carry around RW_NODEBUG - don't be lazy.
>> > - Remove pointless macros.
>> > - Don't make assertions conditional on LOCKDEBUG, there's no reason.
>> > - Make space for a new flag bit (not added yet).
>> >
>> >
>> > To generate a diff of this commit:
>> > cvs rdiff -u -r1.60 -r1.61 src/sys/kern/kern_rwlock.c
>> > cvs rdiff -u -r1.12 -r1.13 src/sys/sys/rwlock.h
>> >
>> > Please note that diffs are not public domain; they are subject to the
>> > copyright notices on the relevant files.
>> >
>> > Modified files:
>> >
>> > Index: src/sys/kern/kern_rwlock.c
>> > diff -u src/sys/kern/kern_rwlock.c:1.60 src/sys/kern/kern_rwlock.c:1.61
>> > --- src/sys/kern/kern_rwlock.c:1.60 Sun Jan 12 18:37:10 2020
>> > +++ src/sys/kern/kern_rwlock.c Sun Jan 19 18:34:24 2020
>> > @@ -1,4 +1,4 @@
>> > -/* $NetBSD: kern_rwlock.c,v 1.60 2020/01/12 18:37:10 ad Exp $
>> > */
>> > +/* $NetBSD: kern_rwlock.c,v 1.61 2020/01/19 18:34:24 ad Exp $
>> > */
>> >
>> > /*-
>> > * Copyright (c) 2002, 2006, 2007, 2008, 2009, 2019, 2020
>> > @@ -39,7 +39,9 @@
>> > */
>> >
>> > #include <sys/cdefs.h>
>> > -__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.60 2020/01/12 18:37:10 ad
>> > Exp $");
>> > +__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.61 2020/01/19 18:34:24 ad
>> > Exp $");
>> > +
>> > +#include "opt_lockdebug.h"
>> >
>> > #define __RWLOCK_PRIVATE
>> >
>> > @@ -63,58 +65,32 @@ __KERNEL_RCSID(0, "$NetBSD: kern_rwlock.
>> > * LOCKDEBUG
>> > */
>> >
>> > -#if defined(LOCKDEBUG)
>> > -
>> > -#define RW_WANTLOCK(rw, op)
>> > \
>> > - LOCKDEBUG_WANTLOCK(RW_DEBUG_P(rw), (rw), \
>> > - (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> > -#define RW_LOCKED(rw, op)
>> > \
>> > - LOCKDEBUG_LOCKED(RW_DEBUG_P(rw), (rw), NULL, \
>> > - (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> > -#define RW_UNLOCKED(rw, op)
>> > \
>> > - LOCKDEBUG_UNLOCKED(RW_DEBUG_P(rw), (rw), \
>> > - (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> > -#define RW_DASSERT(rw, cond)
>> > \
>> > -do {
>> > \
>> > - if (__predict_false(!(cond))) \
>> > - rw_abort(__func__, __LINE__, rw, "assertion failed: " #cond);\
>> > -} while (/* CONSTCOND */ 0);
>> > -
>> > -#else /* LOCKDEBUG */
>> > -
>> > -#define RW_WANTLOCK(rw, op) /* nothing */
>> > -#define RW_LOCKED(rw, op) /* nothing */
>> > -#define RW_UNLOCKED(rw, op) /* nothing */
>> > -#define RW_DASSERT(rw, cond) /* nothing */
>> > +#define RW_DEBUG_P(rw) (((rw)->rw_owner & RW_NODEBUG) == 0)
>> >
>> > -#endif /* LOCKDEBUG */
>> > +#define RW_WANTLOCK(rw, op) \
>> > + LOCKDEBUG_WANTLOCK(RW_DEBUG_P(rw), (rw), \
>> > + (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> > +#define RW_LOCKED(rw, op) \
>> > + LOCKDEBUG_LOCKED(RW_DEBUG_P(rw), (rw), NULL, \
>> > + (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> > +#define RW_UNLOCKED(rw, op) \
>> > + LOCKDEBUG_UNLOCKED(RW_DEBUG_P(rw), (rw), \
>> > + (uintptr_t)__builtin_return_address(0), op == RW_READER);
>> >
>> > /*
>> > * DIAGNOSTIC
>> > */
>> >
>> > #if defined(DIAGNOSTIC)
>> > -
>> > -#define RW_ASSERT(rw, cond)
>> > \
>> > -do {
>> > \
>> > - if (__predict_false(!(cond))) \
>> > +#define RW_ASSERT(rw, cond) \
>> > +do { \
>> > + if (__predict_false(!(cond))) \
>> > rw_abort(__func__, __LINE__, rw, "assertion failed: " #cond);\
>> > } while (/* CONSTCOND */ 0)
>> > -
>> > #else
>> > -
>> > #define RW_ASSERT(rw, cond) /* nothing */
>> > -
>> > #endif /* DIAGNOSTIC */
>> >
>> > -#define RW_SETDEBUG(rw, on) ((rw)->rw_owner |= (on) ? 0 :
>> > RW_NODEBUG)
>> > -#define RW_DEBUG_P(rw) (((rw)->rw_owner & RW_NODEBUG)
>> > == 0)
>> > -#if defined(LOCKDEBUG)
>> > -#define RW_INHERITDEBUG(n, o) (n) |= (o) & RW_NODEBUG
>> > -#else /* defined(LOCKDEBUG) */
>> > -#define RW_INHERITDEBUG(n, o) /* nothing */
>> > -#endif /* defined(LOCKDEBUG) */
>> > -
>> > /*
>> > * Memory barriers.
>> > */
>> > @@ -128,29 +104,6 @@ do {
>> > \
>> > #define RW_MEMBAR_PRODUCER() membar_producer()
>> > #endif
>> >
>> > -static void rw_abort(const char *, size_t, krwlock_t *, const char
>> > *);
>> > -static void rw_dump(const volatile void *, lockop_printer_t);
>> > -static lwp_t *rw_owner(wchan_t);
>> > -
>> > -static inline uintptr_t
>> > -rw_cas(krwlock_t *rw, uintptr_t o, uintptr_t n)
>> > -{
>> > -
>> > - RW_INHERITDEBUG(n, o);
>> > - return (uintptr_t)atomic_cas_ptr((volatile void *)&rw->rw_owner,
>> > - (void *)o, (void *)n);
>> > -}
>> > -
>> > -static inline void
>> > -rw_swap(krwlock_t *rw, uintptr_t o, uintptr_t n)
>> > -{
>> > -
>> > - RW_INHERITDEBUG(n, o);
>> > - n = (uintptr_t)atomic_swap_ptr((volatile void *)&rw->rw_owner,
>> > - (void *)n);
>> > - RW_DASSERT(rw, n == o);
>> > -}
>> > -
>> > /*
>> > * For platforms that do not provide stubs, or for the LOCKDEBUG case.
>> > */
>> > @@ -164,6 +117,10 @@ __strong_alias(rw_exit,rw_vector_exit);
>> > __strong_alias(rw_tryenter,rw_vector_tryenter);
>> > #endif
>> >
>> > +static void rw_abort(const char *, size_t, krwlock_t *, const char
>> > *);
>> > +static void rw_dump(const volatile void *, lockop_printer_t);
>> > +static lwp_t *rw_owner(wchan_t);
>> > +
>> > lockops_t rwlock_lockops = {
>> > .lo_name = "Reader / writer lock",
>> > .lo_type = LOCKOPS_SLEEP,
>> > @@ -179,6 +136,37 @@ syncobj_t rw_syncobj = {
>> > };
>> >
>> > /*
>> > + * rw_cas:
>> > + *
>> > + * Do an atomic compare-and-swap on the lock word.
>> > + */
>> > +static inline uintptr_t
>> > +rw_cas(krwlock_t *rw, uintptr_t o, uintptr_t n)
>> > +{
>> > +
>> > + return (uintptr_t)atomic_cas_ptr((volatile void *)&rw->rw_owner,
>> > + (void *)o, (void *)n);
>> > +}
>> > +
>> > +/*
>> > + * rw_swap:
>> > + *
>> > + * Do an atomic swap of the lock word. This is used only when it's
>> > + * known that the lock word is set up such that it can't be changed
>> > + * behind us (assert this), so there's no point considering the
>> > result.
>> > + */
>> > +static inline void
>> > +rw_swap(krwlock_t *rw, uintptr_t o, uintptr_t n)
>> > +{
>> > +
>> > + n = (uintptr_t)atomic_swap_ptr((volatile void *)&rw->rw_owner,
>> > + (void *)n);
>> > +
>> > + RW_ASSERT(rw, n == o);
>> > + RW_ASSERT(rw, (o & RW_HAS_WAITERS) != 0);
>> > +}
>> > +
>> > +/*
>> > * rw_dump:
>> > *
>> > * Dump the contents of a rwlock structure.
>> > @@ -214,16 +202,14 @@ rw_abort(const char *func, size_t line,
>> > *
>> > * Initialize a rwlock for use.
>> > */
>> > -void _rw_init(krwlock_t *, uintptr_t);
>> > void
>> > _rw_init(krwlock_t *rw, uintptr_t return_address)
>> > {
>> > - bool dodebug;
>> >
>> > - memset(rw, 0, sizeof(*rw));
>> > -
>> > - dodebug = LOCKDEBUG_ALLOC(rw, &rwlock_lockops, return_address);
>> > - RW_SETDEBUG(rw, dodebug);
>> > + if (LOCKDEBUG_ALLOC(rw, &rwlock_lockops, return_address))
>> > + rw->rw_owner = 0;
>> > + else
>> > + rw->rw_owner = RW_NODEBUG;
>> > }
>> >
>> > void
>> > @@ -243,7 +229,7 @@ rw_destroy(krwlock_t *rw)
>> > {
>> >
>> > RW_ASSERT(rw, (rw->rw_owner & ~RW_NODEBUG) == 0);
>> > - LOCKDEBUG_FREE(RW_DEBUG_P(rw), rw);
>> > + LOCKDEBUG_FREE((rw->rw_owner & RW_NODEBUG) == 0, rw);
>> > }
>> >
>> > /*
>> > @@ -327,7 +313,7 @@ rw_vector_enter(krwlock_t *rw, const krw
>> > need_wait = RW_WRITE_LOCKED | RW_WRITE_WANTED;
>> > queue = TS_READER_Q;
>> > } else {
>> > - RW_DASSERT(rw, op == RW_WRITER);
>> > + RW_ASSERT(rw, op == RW_WRITER);
>> > incr = curthread | RW_WRITE_LOCKED;
>> > set_wait = RW_HAS_WAITERS | RW_WRITE_WANTED;
>> > need_wait = RW_WRITE_LOCKED | RW_THREAD;
>> > @@ -430,7 +416,7 @@ rw_vector_enter(krwlock_t *rw, const krw
>> > (uintptr_t)__builtin_return_address(0)));
>> > LOCKSTAT_EXIT(lsflag);
>> >
>> > - RW_DASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
>> > + RW_ASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
>> > (op == RW_READER && RW_COUNT(rw) != 0));
>> > RW_LOCKED(rw, op);
>> > }
>> > @@ -448,7 +434,8 @@ rw_vector_exit(krwlock_t *rw)
>> > int rcnt, wcnt;
>> > lwp_t *l;
>> >
>> > - curthread = (uintptr_t)curlwp;
>> > + l = curlwp;
>> > + curthread = (uintptr_t)l;
>> > RW_ASSERT(rw, curthread != 0);
>> >
>> > /*
>> > @@ -491,8 +478,8 @@ rw_vector_exit(krwlock_t *rw)
>> > */
>> > ts = turnstile_lookup(rw);
>> > owner = rw->rw_owner;
>> > - RW_DASSERT(rw, ts != NULL);
>> > - RW_DASSERT(rw, (owner & RW_HAS_WAITERS) != 0);
>> > + RW_ASSERT(rw, ts != NULL);
>> > + RW_ASSERT(rw, (owner & RW_HAS_WAITERS) != 0);
>> >
>> > wcnt = TS_WAITERS(ts, TS_WRITER_Q);
>> > rcnt = TS_WAITERS(ts, TS_READER_Q);
>> > @@ -509,31 +496,35 @@ rw_vector_exit(krwlock_t *rw)
>> > * do the work of acquiring the lock in rw_vector_enter().
>> > */
>> > if (rcnt == 0 || decr == RW_READ_INCR) {
>> > - RW_DASSERT(rw, wcnt != 0);
>> > - RW_DASSERT(rw, (owner & RW_WRITE_WANTED) != 0);
>> > + RW_ASSERT(rw, wcnt != 0);
>> > + RW_ASSERT(rw, (owner & RW_WRITE_WANTED) != 0);
>> >
>> > if (rcnt != 0) {
>> > /* Give the lock to the longest waiting writer. */
>> > l = TS_FIRST(ts, TS_WRITER_Q);
>> > - newown = (uintptr_t)l | RW_WRITE_LOCKED |
>> > RW_HAS_WAITERS;
>> > + newown = (uintptr_t)l | (owner & RW_NODEBUG);
>> > + newown |= RW_WRITE_LOCKED | RW_HAS_WAITERS;
>> > if (wcnt > 1)
>> > newown |= RW_WRITE_WANTED;
>> > rw_swap(rw, owner, newown);
>> > turnstile_wakeup(ts, TS_WRITER_Q, 1, l);
>> > } else {
>> > /* Wake all writers and let them fight it out. */
>> > - rw_swap(rw, owner, RW_WRITE_WANTED);
>> > + newown = owner & RW_NODEBUG;
>> > + newown |= RW_WRITE_WANTED;
>> > + rw_swap(rw, owner, newown);
>> > turnstile_wakeup(ts, TS_WRITER_Q, wcnt, NULL);
>> > }
>> > } else {
>> > - RW_DASSERT(rw, rcnt != 0);
>> > + RW_ASSERT(rw, rcnt != 0);
>> >
>> > /*
>> > * Give the lock to all blocked readers. If there
>> > * is a writer waiting, new readers that arrive
>> > * after the release will be blocked out.
>> > */
>> > - newown = rcnt << RW_READ_COUNT_SHIFT;
>> > + newown = owner & RW_NODEBUG;
>> > + newown += rcnt << RW_READ_COUNT_SHIFT;
>> > if (wcnt != 0)
>> > newown |= RW_HAS_WAITERS | RW_WRITE_WANTED;
>> >
>> > @@ -552,8 +543,10 @@ int
>> > rw_vector_tryenter(krwlock_t *rw, const krw_t op)
>> > {
>> > uintptr_t curthread, owner, incr, need_wait, next;
>> > + lwp_t *l;
>> >
>> > - curthread = (uintptr_t)curlwp;
>> > + l = curlwp;
>> > + curthread = (uintptr_t)l;
>> >
>> > RW_ASSERT(rw, curthread != 0);
>> >
>> > @@ -561,7 +554,7 @@ rw_vector_tryenter(krwlock_t *rw, const
>> > incr = RW_READ_INCR;
>> > need_wait = RW_WRITE_LOCKED | RW_WRITE_WANTED;
>> > } else {
>> > - RW_DASSERT(rw, op == RW_WRITER);
>> > + RW_ASSERT(rw, op == RW_WRITER);
>> > incr = curthread | RW_WRITE_LOCKED;
>> > need_wait = RW_WRITE_LOCKED | RW_THREAD;
>> > }
>> > @@ -572,24 +565,23 @@ rw_vector_tryenter(krwlock_t *rw, const
>> > next = rw_cas(rw, owner, owner + incr);
>> > if (__predict_true(next == owner)) {
>> > /* Got it! */
>> > - RW_MEMBAR_ENTER();
>> > break;
>> > }
>> > }
>> >
>> > RW_WANTLOCK(rw, op);
>> > RW_LOCKED(rw, op);
>> > - RW_DASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
>> > + RW_ASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
>> > (op == RW_READER && RW_COUNT(rw) != 0));
>> >
>> > + RW_MEMBAR_ENTER();
>> > return 1;
>> > }
>> >
>> > /*
>> > * rw_downgrade:
>> > *
>> > - * Downgrade a write lock to a read lock. Optimise memory
>> > accesses for
>> > - * the uncontended case.
>> > + * Downgrade a write lock to a read lock.
>> > */
>> > void
>> > rw_downgrade(krwlock_t *rw)
>> > @@ -597,55 +589,64 @@ rw_downgrade(krwlock_t *rw)
>> > uintptr_t owner, curthread, newown, next;
>> > turnstile_t *ts;
>> > int rcnt, wcnt;
>> > + lwp_t *l;
>> >
>> > - curthread = (uintptr_t)curlwp;
>> > + l = curlwp;
>> > + curthread = (uintptr_t)l;
>> > RW_ASSERT(rw, curthread != 0);
>> > - RW_DASSERT(rw, (rw->rw_owner & RW_WRITE_LOCKED) != 0);
>> > + RW_ASSERT(rw, (rw->rw_owner & RW_WRITE_LOCKED) != 0);
>> > RW_ASSERT(rw, RW_OWNER(rw) == curthread);
>> > RW_UNLOCKED(rw, RW_WRITER);
>> > #if !defined(DIAGNOSTIC)
>> > __USE(curthread);
>> > #endif
>> >
>> > - /*
>> > - * If there are no waiters, so we can do this the easy way.
>> > - * Try swapping us down to one read hold. If it fails, the
>> > - * lock condition has changed and we most likely now have
>> > - * waiters.
>> > - */
>> > RW_MEMBAR_PRODUCER();
>> > - owner = curthread | RW_WRITE_LOCKED;
>> > - next = rw_cas(rw, owner, RW_READ_INCR);
>> > - if (__predict_true(next == owner)) {
>> > - RW_LOCKED(rw, RW_READER);
>> > - RW_DASSERT(rw, (rw->rw_owner & RW_WRITE_LOCKED) == 0);
>> > - RW_DASSERT(rw, RW_COUNT(rw) != 0);
>> > - return;
>> > - }
>> >
>> > - /*
>> > - * Grab the turnstile chain lock. This gets the interlock
>> > - * on the sleep queue. Once we have that, we can adjust the
>> > - * waiter bits.
>> > - */
>> > - for (;;) {
>> > - owner = next;
>> > + for (owner = rw->rw_owner;; owner = next) {
>> > + /*
>> > + * If there are no waiters we can do this the easy way. Try
>> > + * swapping us down to one read hold. If it fails, the lock
>> > + * condition has changed and we most likely now have
>> > + * waiters.
>> > + */
>> > + if ((owner & RW_HAS_WAITERS) == 0) {
>> > + newown = (owner & RW_NODEBUG);
>> > + next = rw_cas(rw, owner, newown + RW_READ_INCR);
>> > + if (__predict_true(next == owner)) {
>> > + RW_LOCKED(rw, RW_READER);
>> > + RW_ASSERT(rw,
>> > + (rw->rw_owner & RW_WRITE_LOCKED) == 0);
>> > + RW_ASSERT(rw, RW_COUNT(rw) != 0);
>> > + return;
>> > + }
>> > + continue;
>> > + }
>> > +
>> > + /*
>> > + * Grab the turnstile chain lock. This gets the interlock
>> > + * on the sleep queue. Once we have that, we can adjust the
>> > + * waiter bits.
>> > + */
>> > ts = turnstile_lookup(rw);
>> > - RW_DASSERT(rw, ts != NULL);
>> > + RW_ASSERT(rw, ts != NULL);
>> >
>> > rcnt = TS_WAITERS(ts, TS_READER_Q);
>> > wcnt = TS_WAITERS(ts, TS_WRITER_Q);
>> >
>> > - /*
>> > - * If there are no readers, just preserve the waiters
>> > - * bits, swap us down to one read hold and return.
>> > - */
>> > if (rcnt == 0) {
>> > - RW_DASSERT(rw, wcnt != 0);
>> > - RW_DASSERT(rw, (rw->rw_owner & RW_WRITE_WANTED) != 0);
>> > - RW_DASSERT(rw, (rw->rw_owner & RW_HAS_WAITERS) != 0);
>> > -
>> > - newown = RW_READ_INCR | RW_HAS_WAITERS |
>> > RW_WRITE_WANTED;
>> > + /*
>> > + * If there are no readers, just preserve the
>> > + * waiters bits, swap us down to one read hold and
>> > + * return.
>> > + */
>> > + RW_ASSERT(rw, wcnt != 0);
>> > + RW_ASSERT(rw, (rw->rw_owner & RW_WRITE_WANTED) != 0);
>> > + RW_ASSERT(rw, (rw->rw_owner & RW_HAS_WAITERS) != 0);
>> > +
>> > + newown = owner & RW_NODEBUG;
>> > + newown = RW_READ_INCR | RW_HAS_WAITERS |
>> > + RW_WRITE_WANTED;
>> > next = rw_cas(rw, owner, newown);
>> > turnstile_exit(rw);
>> > if (__predict_true(next == owner))
>> > @@ -653,11 +654,12 @@ rw_downgrade(krwlock_t *rw)
>> > } else {
>> > /*
>> > * Give the lock to all blocked readers. We may
>> > - * retain one read hold if downgrading. If there
>> > - * is a writer waiting, new readers will be blocked
>> > + * retain one read hold if downgrading. If there is
>> > + * a writer waiting, new readers will be blocked
>> > * out.
>> > */
>> > - newown = (rcnt << RW_READ_COUNT_SHIFT) + RW_READ_INCR;
>> > + newown = owner & RW_NODEBUG;
>> > + newown += (rcnt << RW_READ_COUNT_SHIFT) + RW_READ_INCR;
>> > if (wcnt != 0)
>> > newown |= RW_HAS_WAITERS | RW_WRITE_WANTED;
>> >
>> > @@ -673,22 +675,24 @@ rw_downgrade(krwlock_t *rw)
>> >
>> > RW_WANTLOCK(rw, RW_READER);
>> > RW_LOCKED(rw, RW_READER);
>> > - RW_DASSERT(rw, (rw->rw_owner & RW_WRITE_LOCKED) == 0);
>> > - RW_DASSERT(rw, RW_COUNT(rw) != 0);
>> > + RW_ASSERT(rw, (rw->rw_owner & RW_WRITE_LOCKED) == 0);
>> > + RW_ASSERT(rw, RW_COUNT(rw) != 0);
>> > }
>> >
>> > /*
>> > * rw_tryupgrade:
>> > *
>> > * Try to upgrade a read lock to a write lock. We must be the only
>> > - * reader. Optimise memory accesses for the uncontended case.
>> > + * reader.
>> > */
>> > int
>> > rw_tryupgrade(krwlock_t *rw)
>> > {
>> > uintptr_t owner, curthread, newown, next;
>> > + struct lwp *l;
>> >
>> > - curthread = (uintptr_t)curlwp;
>> > + l = curlwp;
>> > + curthread = (uintptr_t)l;
>> > RW_ASSERT(rw, curthread != 0);
>> > RW_ASSERT(rw, rw_read_held(rw));
>> >
>> > @@ -709,8 +713,8 @@ rw_tryupgrade(krwlock_t *rw)
>> > RW_UNLOCKED(rw, RW_READER);
>> > RW_WANTLOCK(rw, RW_WRITER);
>> > RW_LOCKED(rw, RW_WRITER);
>> > - RW_DASSERT(rw, rw->rw_owner & RW_WRITE_LOCKED);
>> > - RW_DASSERT(rw, RW_OWNER(rw) == curthread);
>> > + RW_ASSERT(rw, rw->rw_owner & RW_WRITE_LOCKED);
>> > + RW_ASSERT(rw, RW_OWNER(rw) == curthread);
>> >
>> > return 1;
>> > }
>> >
>> > Index: src/sys/sys/rwlock.h
>> > diff -u src/sys/sys/rwlock.h:1.12 src/sys/sys/rwlock.h:1.13
>> > --- src/sys/sys/rwlock.h:1.12 Wed Jan 1 21:34:39 2020
>> > +++ src/sys/sys/rwlock.h Sun Jan 19 18:34:24 2020
>> > @@ -1,7 +1,7 @@
>> > -/* $NetBSD: rwlock.h,v 1.12 2020/01/01 21:34:39 ad Exp $ */
>> > +/* $NetBSD: rwlock.h,v 1.13 2020/01/19 18:34:24 ad Exp $ */
>> >
>> > /*-
>> > - * Copyright (c) 2002, 2006, 2007, 2008, 2019 The NetBSD Foundation, Inc.
>> > + * Copyright (c) 2002, 2006, 2007, 2008, 2019, 2020 The NetBSD
>> > Foundation, Inc.
>> > * All rights reserved.
>> > *
>> > * This code is derived from software contributed to The NetBSD Foundation
>> > @@ -45,10 +45,6 @@
>> > * rw_tryenter()
>> > */
>> >
>> > -#if defined(_KERNEL_OPT)
>> > -#include "opt_lockdebug.h"
>> > -#endif
>> > -
>> > #if !defined(_KERNEL)
>> > #include <sys/types.h>
>> > #include <sys/inttypes.h>
>> > @@ -75,13 +71,9 @@ typedef struct krwlock krwlock_t;
>> > #define RW_HAS_WAITERS 0x01UL /* lock has waiters */
>> > #define RW_WRITE_WANTED 0x02UL /* >= 1 waiter is a writer */
>> > #define RW_WRITE_LOCKED 0x04UL /* lock is currently write
>> > locked */
>> > -#if defined(LOCKDEBUG)
>> > -#define RW_NODEBUG 0x08UL /* LOCKDEBUG disabled */
>> > -#else
>> > -#define RW_NODEBUG 0x00UL /* do nothing */
>> > -#endif /* LOCKDEBUG */
>> > +#define RW_NODEBUG 0x10UL /* LOCKDEBUG disabled */
>> >
>> > -#define RW_READ_COUNT_SHIFT 4
>> > +#define RW_READ_COUNT_SHIFT 5
>> > #define RW_READ_INCR (1UL << RW_READ_COUNT_SHIFT)
>> > #define RW_THREAD ((uintptr_t)-RW_READ_INCR)
>> > #define RW_OWNER(rw) ((rw)->rw_owner & RW_THREAD)
>> > @@ -91,6 +83,7 @@ typedef struct krwlock krwlock_t;
>> > void rw_vector_enter(krwlock_t *, const krw_t);
>> > void rw_vector_exit(krwlock_t *);
>> > int rw_vector_tryenter(krwlock_t *, const krw_t);
>> > +void _rw_init(krwlock_t *, uintptr_t);
>> > #endif /* __RWLOCK_PRIVATE */
>> >
>> > struct krwlock {
>> >
>>
>> --
>> Ryo ONODERA // r...@tetera.org
>> PGP fingerprint = 82A2 DC91 76E0 A10A 8ABB FD1B F404 27FA C7D1 15F3
--
Ryo ONODERA // r...@tetera.org
PGP fingerprint = 82A2 DC91 76E0 A10A 8ABB FD1B F404 27FA C7D1 15F3
