/*
* Acquire a page's "shared/exclusive" lock, but never block.
* Returns 1 on success, 0 on failure.
*/
int
page_trylock(page_t *pp, se_t se)
{
kmutex_t *pse = PAGE_SE_MUTEX(pp);
mutex_enter(pse);
if (pp->p_selock & SE_EWANTED || PP_RETIRED(pp) ||
(se == SE_SHARED && PP_PR_NOSHARE(pp))) {
/*
* Fail if a thread wants exclusive access and page is
* retired, if the page is slated for retirement, or a
* share lock is requested.
*/
mutex_exit(pse);
VM_STAT_ADD(page_trylock_failed);
return (0);
}
if (se == SE_EXCL) {
if (pp->p_selock == 0) {
THREAD_KPRI_REQUEST();
pp->p_selock = SE_WRITER;
mutex_exit(pse);
return (1);
}
} else {
if (pp->p_selock >= 0) {
pp->p_selock += SE_READER;
mutex_exit(pse);
return (1);
}
}
mutex_exit(pse);
return (0);
}
/*
* Test a page to see if it is retired. If errors is non-NULL, the toxic
* bits of the page are returned. Returns 0 on success, error code on failure.
*/
int
page_retire_check_pp(page_t *pp, uint64_t *errors)
{
int rc;
if (PP_RETIRED(pp)) {
PR_DEBUG(prd_checkhit);
rc = 0;
} else if (PP_PR_REQ(pp)) {
PR_DEBUG(prd_checkmiss_pend);
rc = EAGAIN;
} else {
PR_DEBUG(prd_checkmiss_noerr);
rc = EIO;
}
/*
* We have magically arranged the bit values returned to fmd(1M)
* to line up with the FMA, MCE, and UE bits of the page_t.
*/
if (errors) {
uint64_t toxic = (uint64_t)(pp->p_toxic & PR_ERRMASK);
if (toxic & PR_UE_SCRUBBED) {
toxic &= ~PR_UE_SCRUBBED;
toxic |= PR_UE;
}
*errors = toxic;
}
return (rc);
}
/*
* Take a retired page off the retired-pages vnode and clear the toxic flags.
* If "free" is nonzero, lock it and put it back on the freelist. If "free"
* is zero, the caller already holds SE_EXCL lock so we simply unretire it
* and don't do anything else with it.
*
* Any unretire messages are printed from this routine.
*
* Returns 0 if page pp was unretired; else an error code.
*/
int
page_unretire_pp(page_t *pp, int free)
{
/*
* To be retired, a page has to be hashed onto the retired_pages vnode
* and have PR_RETIRED set in p_toxic.
*/
if (free == 0 || page_try_reclaim_lock(pp, SE_EXCL, SE_RETIRED)) {
ASSERT(PAGE_EXCL(pp));
PR_DEBUG(prd_ulocked);
if (!PP_RETIRED(pp)) {
PR_DEBUG(prd_unotretired);
page_unlock(pp);
return (page_retire_done(pp, PRD_UNR_NOT));
}
PR_MESSAGE(CE_NOTE, 1, "unretiring retired"
" page 0x%08x.%08x", mmu_ptob((uint64_t)pp->p_pagenum));
if (pp->p_toxic & PR_FMA) {
PR_DECR_KSTAT(pr_fma);
} else if (pp->p_toxic & PR_UE) {
PR_DECR_KSTAT(pr_ue);
} else {
PR_DECR_KSTAT(pr_mce);
}
page_clrtoxic(pp, PR_ALLFLAGS);
if (free) {
PR_DEBUG(prd_udestroy);
page_destroy(pp, 0);
} else {
PR_DEBUG(prd_uhashout);
page_hashout(pp, NULL);
}
mutex_enter(&freemem_lock);
availrmem++;
mutex_exit(&freemem_lock);
PR_DEBUG(prd_uunretired);
PR_DECR_KSTAT(pr_retired);
PR_INCR_KSTAT(pr_unretired);
return (page_retire_done(pp, PRD_UNR_SUCCESS));
}
PR_DEBUG(prd_unotlocked);
return (page_retire_done(pp, PRD_UNR_CANTLOCK));
}
/*
* Release the page's "shared/exclusive" lock and wake up anyone
* who might be waiting for it.
*/
void
page_unlock(page_t *pp)
{
kmutex_t *pse = PAGE_SE_MUTEX(pp);
selock_t old;
mutex_enter(pse);
old = pp->p_selock;
if ((old & ~SE_EWANTED) == SE_READER) {
pp->p_selock = old & ~SE_READER;
if (CV_HAS_WAITERS(&pp->p_cv))
cv_broadcast(&pp->p_cv);
} else if ((old & ~SE_EWANTED) == SE_DELETED) {
panic("page_unlock: page %p is deleted", pp);
} else if (old < 0) {
THREAD_KPRI_RELEASE();
pp->p_selock &= SE_EWANTED;
if (CV_HAS_WAITERS(&pp->p_cv))
cv_broadcast(&pp->p_cv);
} else if ((old & ~SE_EWANTED) > SE_READER) {
pp->p_selock = old - SE_READER;
} else {
panic("page_unlock: page %p is not locked", pp);
}
if (pp->p_selock == 0) {
/*
* If the T_CAPTURING bit is set, that means that we should
* not try and capture the page again as we could recurse
* which could lead to a stack overflow panic or spending a
* relatively long time in the kernel making no progress.
*/
if ((pp->p_toxic & PR_CAPTURE) &&
!(curthread->t_flag & T_CAPTURING) &&
!PP_RETIRED(pp)) {
THREAD_KPRI_REQUEST();
pp->p_selock = SE_WRITER;
mutex_exit(pse);
page_unlock_capture(pp);
} else {
mutex_exit(pse);
}
} else {
mutex_exit(pse);
}
}
/*
* On a reboot, our friend mdboot() wants to clear up any PP_PR_REQ() pages
* that we were not able to retire. On large machines, walking the complete
* page_t array and looking at every page_t takes too long. So, as a page is
* marked toxic, we track it using a list that can be processed at reboot
* time. page_retire_enqueue() will do its best to try to avoid duplicate
* entries, but if we get too many errors at once the queue can overflow,
* in which case we will end up walking every page_t as a last resort.
* The background thread also makes use of this queue to find which pages
* are pending retirement.
*/
static void
page_retire_enqueue(page_t *pp)
{
int nslot = -1;
int i;
mutex_enter(&pr_q_mutex);
/*
* Check to make sure retire hasn't already dequeued it.
* In the meantime if the page was cleaned up, no need
* to enqueue it.
*/
if (PP_RETIRED(pp) || pp->p_toxic == 0) {
mutex_exit(&pr_q_mutex);
PR_DEBUG(prd_noaction);
return;
}
for (i = 0; i < PR_PENDING_QMAX; i++) {
if (pr_pending_q[i] == pp) {
mutex_exit(&pr_q_mutex);
PR_DEBUG(prd_qdup);
return;
} else if (nslot == -1 && pr_pending_q[i] == NULL) {
nslot = i;
}
}
PR_INCR_KSTAT(pr_pending);
if (nslot != -1) {
pr_pending_q[nslot] = pp;
PR_DEBUG(prd_queued);
} else {
PR_INCR_KSTAT(pr_enqueue_fail);
PR_DEBUG(prd_notqueued);
}
mutex_exit(&pr_q_mutex);
}
/*
* page_retire() - the front door in to retire a page.
*
* Ideally, page_retire() would instantly retire the requested page.
* Unfortunately, some pages are locked or otherwise tied up and cannot be
* retired right away. To deal with that, bits are set in p_toxic of the
* page_t. An attempt is made to lock the page; if the attempt is successful,
* we instantly unlock the page counting on page_unlock() to notice p_toxic
* is nonzero and to call back into page_retire_pp(). Success is determined
* by looking to see whether the page has been retired once it has been
* unlocked.
*
* Returns:
*
* - 0 on success,
* - EINVAL when the PA is whacko,
* - EIO if the page is already retired or already pending retirement, or
* - EAGAIN if the page could not be _immediately_ retired but is pending.
*/
int
page_retire(uint64_t pa, uchar_t reason)
{
page_t *pp;
ASSERT(reason & PR_REASONS); /* there must be a reason */
ASSERT(!(reason & ~PR_REASONS)); /* but no other bits */
pp = page_numtopp_nolock(mmu_btop(pa));
if (pp == NULL) {
PR_MESSAGE(CE_WARN, 1, "Cannot schedule clearing of error on"
" page 0x%08x.%08x; page is not relocatable memory", pa);
return (page_retire_done(pp, PRD_INVALID_PA));
}
if (PP_RETIRED(pp)) {
PR_DEBUG(prd_dup1);
return (page_retire_done(pp, PRD_DUPLICATE));
}
if ((reason & PR_UE) && !PP_TOXIC(pp)) {
PR_MESSAGE(CE_NOTE, 1, "Scheduling clearing of error on"
" page 0x%08x.%08x", pa);
} else if (PP_PR_REQ(pp)) {
PR_DEBUG(prd_dup2);
return (page_retire_done(pp, PRD_DUPLICATE));
} else {
PR_MESSAGE(CE_NOTE, 1, "Scheduling removal of"
" page 0x%08x.%08x", pa);
}
page_settoxic(pp, reason);
page_retire_enqueue(pp);
/*
* And now for some magic.
*
* We marked this page toxic up above. All there is left to do is
* to try to lock the page and then unlock it. The page lock routines
* will intercept the page and retire it if they can. If the page
* cannot be locked, 's okay -- page_unlock() will eventually get it,
* or the background thread, until then the lock routines will deny
* further locks on it.
*/
if (MTBF(pr_calls, pr_mtbf) && page_trylock(pp, SE_EXCL)) {
PR_DEBUG(prd_prlocked);
page_unlock(pp);
} else {
PR_DEBUG(prd_prnotlocked);
}
if (PP_RETIRED(pp)) {
PR_DEBUG(prd_prretired);
return (0);
} else {
cv_signal(&pr_cv);
PR_INCR_KSTAT(pr_failed);
if (pp->p_toxic & PR_MSG) {
return (page_retire_done(pp, PRD_FAILED));
} else {
return (page_retire_done(pp, PRD_PENDING));
}
}
}
/*
* Read the comments inside of page_lock_es() carefully.
*
* SE_EXCL callers specifying es == SE_EXCL_WANTED will cause the
* SE_EWANTED bit of p_selock to be set when the lock cannot be obtained.
* This is used by threads subject to reader-starvation (eg. memory delete).
*
* When a thread using SE_EXCL_WANTED does not obtain the SE_EXCL lock,
* it is expected that it will retry at a later time. Threads that will
* not retry the lock *must* call page_lock_clr_exclwanted to clear the
* SE_EWANTED bit. (When a thread using SE_EXCL_WANTED obtains the lock,
* the bit is cleared.)
*/
int
page_try_reclaim_lock(page_t *pp, se_t se, int es)
{
kmutex_t *pse = PAGE_SE_MUTEX(pp);
selock_t old;
mutex_enter(pse);
old = pp->p_selock;
ASSERT(((es & SE_EXCL_WANTED) == 0) ||
((es & SE_EXCL_WANTED) && (se == SE_EXCL)));
if (PP_RETIRED(pp) && !(es & SE_RETIRED)) {
mutex_exit(pse);
VM_STAT_ADD(page_trylock_failed);
return (0);
}
if (se == SE_SHARED && es == 1 && old == 0) {
se = SE_EXCL;
}
if (se == SE_SHARED) {
if (!PP_ISFREE(pp)) {
if (old >= 0) {
/*
* Readers are not allowed when excl wanted
*/
if ((old & SE_EWANTED) == 0) {
pp->p_selock = old + SE_READER;
mutex_exit(pse);
return (1);
}
}
mutex_exit(pse);
return (0);
}
/*
* The page is free, so we really want SE_EXCL (below)
*/
VM_STAT_ADD(page_try_reclaim_upgrade);
}
/*
* The caller wants a writer lock. We try for it only if
* SE_EWANTED is not set, or if the caller specified
* SE_EXCL_WANTED.
*/
if (!(old & SE_EWANTED) || (es & SE_EXCL_WANTED)) {
if ((old & ~SE_EWANTED) == 0) {
/* no reader/writer lock held */
THREAD_KPRI_REQUEST();
/* this clears out our setting of the SE_EWANTED bit */
pp->p_selock = SE_WRITER;
mutex_exit(pse);
return (1);
}
}
if (es & SE_EXCL_WANTED) {
/* page is locked, set the SE_EWANTED bit */
pp->p_selock |= SE_EWANTED;
}
mutex_exit(pse);
return (0);
}
/*
* With the addition of reader-writer lock semantics to page_lock_es,
* callers wanting an exclusive (writer) lock may prevent shared-lock
* (reader) starvation by setting the es parameter to SE_EXCL_WANTED.
* In this case, when an exclusive lock cannot be acquired, p_selock's
* SE_EWANTED bit is set. Shared-lock (reader) requests are also denied
* if the page is slated for retirement.
*
* The se and es parameters determine if the lock should be granted
* based on the following decision table:
*
* Lock wanted es flags p_selock/SE_EWANTED Action
* ----------- -------------- ------------------- ---------
* SE_EXCL any [1][2] unlocked/any grant lock, clear SE_EWANTED
* SE_EXCL SE_EWANTED any lock/any deny, set SE_EWANTED
* SE_EXCL none any lock/any deny
* SE_SHARED n/a [2] shared/0 grant
* SE_SHARED n/a [2] unlocked/0 grant
* SE_SHARED n/a shared/1 deny
* SE_SHARED n/a unlocked/1 deny
* SE_SHARED n/a excl/any deny
*
* Notes:
* [1] The code grants an exclusive lock to the caller and clears the bit
* SE_EWANTED whenever p_selock is unlocked, regardless of the SE_EWANTED
* bit's value. This was deemed acceptable as we are not concerned about
* exclusive-lock starvation. If this ever becomes an issue, a priority or
* fifo mechanism should also be implemented. Meantime, the thread that
* set SE_EWANTED should be prepared to catch this condition and reset it
*
* [2] Retired pages may not be locked at any time, regardless of the
* dispostion of se, unless the es parameter has SE_RETIRED flag set.
*
* Notes on values of "es":
*
* es & 1: page_lookup_create will attempt page relocation
* es & SE_EXCL_WANTED: caller wants SE_EWANTED set (eg. delete
* memory thread); this prevents reader-starvation of waiting
* writer thread(s) by giving priority to writers over readers.
* es & SE_RETIRED: caller wants to lock pages even if they are
* retired. Default is to deny the lock if the page is retired.
*
* And yes, we know, the semantics of this function are too complicated.
* It's on the list to be cleaned up.
*/
int
page_lock_es(page_t *pp, se_t se, kmutex_t *lock, reclaim_t reclaim, int es)
{
int retval;
kmutex_t *pse = PAGE_SE_MUTEX(pp);
int upgraded;
int reclaim_it;
ASSERT(lock != NULL ? MUTEX_HELD(lock) : 1);
VM_STAT_ADD(page_lock_count);
upgraded = 0;
reclaim_it = 0;
mutex_enter(pse);
ASSERT(((es & SE_EXCL_WANTED) == 0) ||
((es & SE_EXCL_WANTED) && (se == SE_EXCL)));
if (PP_RETIRED(pp) && !(es & SE_RETIRED)) {
mutex_exit(pse);
VM_STAT_ADD(page_lock_retired);
return (0);
}
if (se == SE_SHARED && es == 1 && pp->p_selock == 0) {
se = SE_EXCL;
}
if ((reclaim == P_RECLAIM) && (PP_ISFREE(pp))) {
reclaim_it = 1;
if (se == SE_SHARED) {
/*
* This is an interesting situation.
*
* Remember that p_free can only change if
* p_selock < 0.
* p_free does not depend on our holding `pse'.
* And, since we hold `pse', p_selock can not change.
* So, if p_free changes on us, the page is already
* exclusively held, and we would fail to get p_selock
* regardless.
*
* We want to avoid getting the share
* lock on a free page that needs to be reclaimed.
* It is possible that some other thread has the share
* lock and has left the free page on the cache list.
* pvn_vplist_dirty() does this for brief periods.
* If the se_share is currently SE_EXCL, we will fail
* to acquire p_selock anyway. Blocking is the
* right thing to do.
* If we need to reclaim this page, we must get
* exclusive access to it, force the upgrade now.
* Again, we will fail to acquire p_selock if the
* page is not free and block.
*/
upgraded = 1;
se = SE_EXCL;
VM_STAT_ADD(page_lock_upgrade);
}
}
if (se == SE_EXCL) {
if (!(es & SE_EXCL_WANTED) && (pp->p_selock & SE_EWANTED)) {
/*
* if the caller wants a writer lock (but did not
* specify exclusive access), and there is a pending
* writer that wants exclusive access, return failure
*/
retval = 0;
} else if ((pp->p_selock & ~SE_EWANTED) == 0) {
/* no reader/writer lock held */
THREAD_KPRI_REQUEST();
/* this clears our setting of the SE_EWANTED bit */
pp->p_selock = SE_WRITER;
retval = 1;
} else {
/* page is locked */
if (es & SE_EXCL_WANTED) {
/* set the SE_EWANTED bit */
pp->p_selock |= SE_EWANTED;
}
retval = 0;
}
} else {
retval = 0;
if (pp->p_selock >= 0) {
if ((pp->p_selock & SE_EWANTED) == 0) {
pp->p_selock += SE_READER;
retval = 1;
}
}
}
if (retval == 0) {
if ((pp->p_selock & ~SE_EWANTED) == SE_DELETED) {
VM_STAT_ADD(page_lock_deleted);
mutex_exit(pse);
return (retval);
}
#ifdef VM_STATS
VM_STAT_ADD(page_lock_miss);
if (upgraded) {
VM_STAT_ADD(page_lock_upgrade_failed);
}
#endif
if (lock) {
VM_STAT_ADD(page_lock_miss_lock);
mutex_exit(lock);
}
/*
* Now, wait for the page to be unlocked and
* release the lock protecting p_cv and p_selock.
*/
cv_wait(&pp->p_cv, pse);
mutex_exit(pse);
/*
* The page identity may have changed while we were
* blocked. If we are willing to depend on "pp"
* still pointing to a valid page structure (i.e.,
* assuming page structures are not dynamically allocated
* or freed), we could try to lock the page if its
* identity hasn't changed.
*
* This needs to be measured, since we come back from
* cv_wait holding pse (the expensive part of this
* operation) we might as well try the cheap part.
* Though we would also have to confirm that dropping
* `lock' did not cause any grief to the callers.
*/
if (lock) {
mutex_enter(lock);
}
} else {
/*
* We have the page lock.
* If we needed to reclaim the page, and the page
* needed reclaiming (ie, it was free), then we
* have the page exclusively locked. We may need
* to downgrade the page.
*/
ASSERT((upgraded) ?
((PP_ISFREE(pp)) && PAGE_EXCL(pp)) : 1);
mutex_exit(pse);
/*
* We now hold this page's lock, either shared or
* exclusive. This will prevent its identity from changing.
* The page, however, may or may not be free. If the caller
* requested, and it is free, go reclaim it from the
* free list. If the page can't be reclaimed, return failure
* so that the caller can start all over again.
*
* NOTE:page_reclaim() releases the page lock (p_selock)
* if it can't be reclaimed.
*/
if (reclaim_it) {
if (!page_reclaim(pp, lock)) {
VM_STAT_ADD(page_lock_bad_reclaim);
retval = 0;
} else {
VM_STAT_ADD(page_lock_reclaim);
if (upgraded) {
page_downgrade(pp);
}
}
}
}
return (retval);
}
