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fix implicit locktype escalation

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This commit is contained in:
Keagan McClelland
2021-12-20 17:39:13 -07:00
committed by Aiden McClelland
parent 0860275869
commit 70dc690437
1 changed files with 61 additions and 26 deletions
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87
patch-db/src/locker.rs
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@@ -315,6 +315,16 @@ impl LockOrderEnforcer {
} }
// locks must be acquired in lexicographic order for the pointer, and reverse order for type // locks must be acquired in lexicographic order for the pointer, and reverse order for type
fn validate(&self, req: &LockInfo) -> Result<(), LockError> { fn validate(&self, req: &LockInfo) -> Result<(), LockError> {
// the following notation is used to denote an example sequence that can cause deadlocks
//
// Individual Lock Requests
// 1W/A/B
// |||> Node whose lock is being acquired: /A/B (strings prefixed by slashes, indicating descent path)
// ||> Type of Lock: W (E/R/W)
// |> Session Number: 1 (any natural number)
//
// Sequences
// LockRequest >> LockRequest
match self.locks_held.get(&req.handle_id) { match self.locks_held.get(&req.handle_id) {
None => Ok(()), None => Ok(()),
Some(m) => { Some(m) => {
@@ -329,35 +339,52 @@ impl LockOrderEnforcer {
return Ok(()); return Ok(());
} }
} }
let err = m.keys().find_map(|(ptr, ty)| { let err = m.keys().find_map(|(ptr, ty)| match ptr.cmp(&req.ptr) {
match ptr.cmp(&req.ptr) { std::cmp::Ordering::Less => {
std::cmp::Ordering::Less => None, // this is OK if req.ptr.starts_with(ptr)
std::cmp::Ordering::Equal => { && req.ty == LockType::Write
if req.ty > *ty { && *ty == LockType::Read
Some(LockError::LockTypeEscalation { {
session: req.handle_id.clone(), // 1R/A >> 2R/A >> 1W/A/A >> 2W/A/B
ptr: ptr.clone(), Some(LockError::LockTypeEscalationImplicit {
first: *ty,
second: req.ty,
})
} else {
None
}
}
std::cmp::Ordering::Greater => Some(if ptr.starts_with(&req.ptr) {
LockError::LockTaxonomyEscalation {
session: req.handle_id.clone(), session: req.handle_id.clone(),
first: ptr.clone(), first_ptr: ptr.clone(),
second: req.ptr.clone(), first_type: *ty,
} second_ptr: req.ptr.clone(),
second_type: req.ty,
})
} else { } else {
LockError::NonCanonicalOrdering { None
session: req.handle_id.clone(), }
first: ptr.clone(),
second: req.ptr.clone(),
}
}),
} }
std::cmp::Ordering::Equal => {
if req.ty > *ty {
// 1R/A >> 2R/A >> 1W/A >> 1W/A
Some(LockError::LockTypeEscalation {
session: req.handle_id.clone(),
ptr: ptr.clone(),
first: *ty,
second: req.ty,
})
} else {
None
}
}
std::cmp::Ordering::Greater => Some(if ptr.starts_with(&req.ptr) {
// 1W/A/A >> 2W/A/B >> 1R/A >> 2R/A
LockError::LockTaxonomyEscalation {
session: req.handle_id.clone(),
first: ptr.clone(),
second: req.ptr.clone(),
}
} else {
// 1W/A >> 2W/B >> 1W/B >> 2W/A
LockError::NonCanonicalOrdering {
session: req.handle_id.clone(),
first: ptr.clone(),
second: req.ptr.clone(),
}
}),
}); });
err.map_or(Ok(()), Err) err.map_or(Ok(()), Err)
} }
@@ -1064,6 +1091,14 @@ pub enum LockError {
first: LockType, first: LockType,
second: LockType, second: LockType,
}, },
#[error("Lock Type Escalation Implicit: Session = {session:?}, First = {first_ptr}:{first_type}, Second = {second_ptr}:{second_type}")]
LockTypeEscalationImplicit {
session: HandleId,
first_ptr: JsonPointer,
first_type: LockType,
second_ptr: JsonPointer,
second_type: LockType,
},
#[error( #[error(
"Non-Canonical Lock Ordering: Session = {session:?}, First = {first}, Second = {second}" "Non-Canonical Lock Ordering: Session = {session:?}, First = {first}, Second = {second}"
)] )]