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preserve context per request for local locks (#9828)

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In the Current bug we were re-using the context
from previously granted lockers, this would
lead to lock timeouts for existing valid
read or write locks, leading to premature
timeout of locks.

This bug affects only local lockers in FS
or standalone erasure coded mode. This issue
is rather historical as well and was present
in lsync for some time but we were lucky to
not see it.

Similar changes are done in dsync as well
to keep the code more familiar

Fixes #9827
This commit is contained in:
Harshavardhana
2020-06-14 07:43:10 -07:00
committed by GitHub
parent 535efd34a0
commit d55f4336ae
6 changed files with 103 additions and 111 deletions
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70
pkg/lsync/lrwmutex.go
View File

@@ -32,12 +32,11 @@ type LRWMutex struct {
isWriteLock bool
ref int
m sync.Mutex // Mutex to prevent multiple simultaneous locks
ctx context.Context
}
// NewLRWMutex - initializes a new lsync RW mutex.
func NewLRWMutex(ctx context.Context) *LRWMutex {
return &LRWMutex{ctx: ctx}
func NewLRWMutex() *LRWMutex {
return &LRWMutex{}
}
// Lock holds a write lock on lm.
@@ -47,14 +46,14 @@ func NewLRWMutex(ctx context.Context) *LRWMutex {
func (lm *LRWMutex) Lock() {
const isWriteLock = true
lm.lockLoop(lm.id, lm.source, time.Duration(math.MaxInt64), isWriteLock)
lm.lockLoop(context.Background(), lm.id, lm.source, time.Duration(math.MaxInt64), isWriteLock)
}
// GetLock tries to get a write lock on lm before the timeout occurs.
func (lm *LRWMutex) GetLock(id string, source string, timeout time.Duration) (locked bool) {
func (lm *LRWMutex) GetLock(ctx context.Context, id string, source string, timeout time.Duration) (locked bool) {
const isWriteLock = true
return lm.lockLoop(id, source, timeout, isWriteLock)
return lm.lockLoop(ctx, id, source, timeout, isWriteLock)
}
// RLock holds a read lock on lm.
@@ -64,60 +63,55 @@ func (lm *LRWMutex) GetLock(id string, source string, timeout time.Duration) (lo
func (lm *LRWMutex) RLock() {
const isWriteLock = false
lm.lockLoop(lm.id, lm.source, time.Duration(1<<63-1), isWriteLock)
lm.lockLoop(context.Background(), lm.id, lm.source, time.Duration(1<<63-1), isWriteLock)
}
// GetRLock tries to get a read lock on lm before the timeout occurs.
func (lm *LRWMutex) GetRLock(id string, source string, timeout time.Duration) (locked bool) {
func (lm *LRWMutex) GetRLock(ctx context.Context, id string, source string, timeout time.Duration) (locked bool) {
const isWriteLock = false
return lm.lockLoop(id, source, timeout, isWriteLock)
return lm.lockLoop(ctx, id, source, timeout, isWriteLock)
}
func (lm *LRWMutex) lock(id, source string, isWriteLock bool) (locked bool) {
lm.m.Lock()
lm.id = id
lm.source = source
if isWriteLock {
if lm.ref == 0 && !lm.isWriteLock {
lm.ref = 1
lm.isWriteLock = true
locked = true
}
} else {
if !lm.isWriteLock {
lm.ref++
locked = true
}
}
lm.m.Unlock()
return locked
}
// lockLoop will acquire either a read or a write lock
//
// The call will block until the lock is granted using a built-in
// timing randomized back-off algorithm to try again until successful
func (lm *LRWMutex) lockLoop(id, source string, timeout time.Duration, isWriteLock bool) bool {
retryCtx, cancel := context.WithTimeout(lm.ctx, timeout)
func (lm *LRWMutex) lockLoop(ctx context.Context, id, source string, timeout time.Duration, isWriteLock bool) (locked bool) {
retryCtx, cancel := context.WithTimeout(ctx, timeout)
defer cancel()
// We timed out on the previous lock, incrementally wait
// for a longer back-off time and try again afterwards.
for range retry.NewTimer(retryCtx) {
// Try to acquire the lock.
var success bool
{
lm.m.Lock()
lm.id = id
lm.source = source
if isWriteLock {
if lm.ref == 0 && !lm.isWriteLock {
lm.ref = 1
lm.isWriteLock = true
success = true
}
} else {
if !lm.isWriteLock {
lm.ref++
success = true
}
}
lm.m.Unlock()
}
if success {
if lm.lock(id, source, isWriteLock) {
return true
}
}
// We timed out on the previous lock, incrementally wait
// for a longer back-off time and try again afterwards.
return false
}