detached 464d66c

fix(fdwait): remove epoll watches before descriptors can close

commit
464d66cb9a69d04f6c942036dc3dfd59436d27a6
author
brice · · 2026-10-13 20:40 UTC
parent
ea0e1c7
signature
GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email
refs
proto/netpoll-waits
3 files · +88 -40
Unified
UnifiedSplit
A internal/adapters/fdwait/duplicate_test.go +60 -0
@@ -0,0 +1,60 @@
1+package fdwait
2+
3+import (
4+ "golang.org/x/sys/unix"
5+ "testing"
6+ "time"
7+)
8+
9+// Epoll retains a registration after its fd closes if another descriptor
10+// still refers to the same open file description.
11+func TestRemovedDuplicatedDescriptorDoesNotKeepPollReadable(t *testing.T) {
12+ p, err := New()
13+ if err != nil {
14+ t.Fatal(err)
15+ }
16+ defer p.Close()
17+ old, err := unix.Eventfd(0, unix.EFD_NONBLOCK|unix.EFD_CLOEXEC)
18+ if err != nil {
19+ t.Fatal(err)
20+ }
21+ dup, err := unix.Dup(old)
22+ if err != nil {
23+ unix.Close(old)
24+ t.Fatal(err)
25+ }
26+ defer unix.Close(dup)
27+ if _, err := p.Poll([]unix.PollFd{{Fd: int32(old), Events: unix.POLLIN}}, 1); err != nil {
28+ t.Fatal(err)
29+ }
30+ // Create the next descriptor before closing old so its number is not
31+ // reused. This leaves an old epoll registration with no usable fd.
32+ fresh, err := unix.Eventfd(0, unix.EFD_NONBLOCK|unix.EFD_CLOEXEC)
33+ if err != nil {
34+ t.Fatal(err)
35+ }
36+ defer unix.Close(fresh)
37+ unix.Close(old)
38+ if _, err := unix.Write(dup, []byte{1, 0, 0, 0, 0, 0, 0, 0}); err != nil {
39+ t.Fatal(err)
40+ }
41+ if err := p.raw.Control(func(ep uintptr) {
42+ var events [1]unix.EpollEvent
43+ if n, err := unix.EpollWait(int(ep), events[:], 0); n != 0 || err != nil {
44+ t.Errorf("closed watched descriptor still makes epoll readable: %d %v", n, err)
45+ }
46+ }); err != nil {
47+ t.Fatal(err)
48+ }
49+ done := make(chan error, 1)
50+ go func() { _, err := p.Poll([]unix.PollFd{{Fd: int32(fresh), Events: unix.POLLIN}}, 20); done <- err }()
51+ select {
52+ case err := <-done:
53+ if err != nil {
54+ t.Fatal(err)
55+ }
56+ case <-time.After(time.Second):
57+ p.Close()
58+ t.Fatal("stale epoll readiness prevents timeout")
59+ }
60+}
@@ -0,0 +1,60 @@
1+package fdwait
2+
3+import (
4+ "golang.org/x/sys/unix"
5+ "testing"
6+ "time"
7+)
8+
9+// Epoll retains a registration after its fd closes if another descriptor
10+// still refers to the same open file description.
11+func TestRemovedDuplicatedDescriptorDoesNotKeepPollReadable(t *testing.T) {
12+ p, err := New()
13+ if err != nil {
14+ t.Fatal(err)
15+ }
16+ defer p.Close()
17+ old, err := unix.Eventfd(0, unix.EFD_NONBLOCK|unix.EFD_CLOEXEC)
18+ if err != nil {
19+ t.Fatal(err)
20+ }
21+ dup, err := unix.Dup(old)
22+ if err != nil {
23+ unix.Close(old)
24+ t.Fatal(err)
25+ }
26+ defer unix.Close(dup)
27+ if _, err := p.Poll([]unix.PollFd{{Fd: int32(old), Events: unix.POLLIN}}, 1); err != nil {
28+ t.Fatal(err)
29+ }
30+ // Create the next descriptor before closing old so its number is not
31+ // reused. This leaves an old epoll registration with no usable fd.
32+ fresh, err := unix.Eventfd(0, unix.EFD_NONBLOCK|unix.EFD_CLOEXEC)
33+ if err != nil {
34+ t.Fatal(err)
35+ }
36+ defer unix.Close(fresh)
37+ unix.Close(old)
38+ if _, err := unix.Write(dup, []byte{1, 0, 0, 0, 0, 0, 0, 0}); err != nil {
39+ t.Fatal(err)
40+ }
41+ if err := p.raw.Control(func(ep uintptr) {
42+ var events [1]unix.EpollEvent
43+ if n, err := unix.EpollWait(int(ep), events[:], 0); n != 0 || err != nil {
44+ t.Errorf("closed watched descriptor still makes epoll readable: %d %v", n, err)
45+ }
46+ }); err != nil {
47+ t.Fatal(err)
48+ }
49+ done := make(chan error, 1)
50+ go func() { _, err := p.Poll([]unix.PollFd{{Fd: int32(fresh), Events: unix.POLLIN}}, 20); done <- err }()
51+ select {
52+ case err := <-done:
53+ if err != nil {
54+ t.Fatal(err)
55+ }
56+ case <-time.After(time.Second):
57+ p.Close()
58+ t.Fatal("stale epoll readiness prevents timeout")
59+ }
60+}
M internal/adapters/fdwait/poller.go +21 -38
@@ -13,9 +13,8 @@ import (
1313 // Poller owns an epoll descriptor and is used by one goroutine.
1414 // Watched descriptors remain owned by the caller.
1515 type Poller struct {
16- file *os.File
17- raw syscall.RawConn
18- registered map[int]struct{}
16+ file *os.File
17+ raw syscall.RawConn
1918 }
2019
2120 func New() (*Poller, error) {
@@ -33,52 +32,36 @@ func New() (*Poller, error) {
3332 f.Close()
3433 return nil, err
3534 }
36- return &Poller{file: f, raw: raw, registered: make(map[int]struct{})}, nil
35+ return &Poller{file: f, raw: raw}, nil
3736 }
38-
3937 func (p *Poller) Close() error { return p.file.Close() }
4038
41-// Poll has the readable/error semantics of unix.Poll. A negative timeout
42-// waits indefinitely. Timeout expiration returns zero, not an error.
39+// Poll waits for readable/error events. It never consumes caller events.
40+// Each call explicitly removes its epoll registrations before the caller can
41+// close or recycle watched fds. Relying on close to remove them is unsafe:
42+// another fd or a kernel fence may retain the open file description.
4343 func (p *Poller) Poll(fds []unix.PollFd, timeout int) (int, error) {
44- // Remove registrations no longer requested. Closing a watched fd already
45- // removes it from epoll, so ENOENT and EBADF are harmless here.
46- err := p.raw.Control(func(ep uintptr) {
47- for fd := range p.registered {
48- found := false
49- for _, f := range fds {
50- if int(f.Fd) == fd {
51- found = true
52- break
53- }
54- }
55- if !found {
56- unix.EpollCtl(int(ep), unix.EPOLL_CTL_DEL, fd, nil)
57- delete(p.registered, fd)
58- }
59- }
60- })
61- if err != nil {
62- return 0, err
63- }
6444 var ctlErr error
65- err = p.raw.Control(func(ep uintptr) {
45+ added := 0
46+ err := p.raw.Control(func(ep uintptr) {
6647 for _, f := range fds {
67- fd := int(f.Fd)
68- if fd < 0 {
48+ if f.Fd < 0 {
49+ added++
6950 continue
7051 }
71- // MOD detects a descriptor number recycled after its old file closed.
72- ev := unix.EpollEvent{Events: unix.EPOLLIN, Fd: int32(fd)}
73- e := unix.EpollCtl(int(ep), unix.EPOLL_CTL_MOD, fd, &ev)
74- if errors.Is(e, unix.ENOENT) {
75- e = unix.EpollCtl(int(ep), unix.EPOLL_CTL_ADD, fd, &ev)
76- }
77- if e != nil {
52+ ev := unix.EpollEvent{Events: unix.EPOLLIN, Fd: f.Fd}
53+ if e := unix.EpollCtl(int(ep), unix.EPOLL_CTL_ADD, int(f.Fd), &ev); e != nil {
7854 ctlErr = e
7955 return
8056 }
81- p.registered[fd] = struct{}{}
57+ added++
58+ }
59+ })
60+ defer p.raw.Control(func(ep uintptr) {
61+ for _, f := range fds[:added] {
62+ if f.Fd >= 0 {
63+ unix.EpollCtl(int(ep), unix.EPOLL_CTL_DEL, int(f.Fd), nil)
64+ }
8265 }
8366 })
8467 if err != nil {
@@ -13,9 +13,8 @@ import (
13 // Poller owns an epoll descriptor and is used by one goroutine.13 // Poller owns an epoll descriptor and is used by one goroutine.
14 // Watched descriptors remain owned by the caller.14 // Watched descriptors remain owned by the caller.
15 type Poller struct {15 type Poller struct {
16- file *os.File16+ file *os.File
17- raw syscall.RawConn17+ raw syscall.RawConn
18- registered map[int]struct{}
19 }18 }
20 19
21 func New() (*Poller, error) {20 func New() (*Poller, error) {
@@ -33,52 +32,36 @@ func New() (*Poller, error) {
33 f.Close()32 f.Close()
34 return nil, err33 return nil, err
35 }34 }
36- return &Poller{file: f, raw: raw, registered: make(map[int]struct{})}, nil35+ return &Poller{file: f, raw: raw}, nil
37 }36 }
38-
39 func (p *Poller) Close() error { return p.file.Close() }37 func (p *Poller) Close() error { return p.file.Close() }
40 38
41-// Poll has the readable/error semantics of unix.Poll. A negative timeout39+// Poll waits for readable/error events. It never consumes caller events.
42-// waits indefinitely. Timeout expiration returns zero, not an error.40+// Each call explicitly removes its epoll registrations before the caller can
41+// close or recycle watched fds. Relying on close to remove them is unsafe:
42+// another fd or a kernel fence may retain the open file description.
43 func (p *Poller) Poll(fds []unix.PollFd, timeout int) (int, error) {43 func (p *Poller) Poll(fds []unix.PollFd, timeout int) (int, error) {
44- // Remove registrations no longer requested. Closing a watched fd already
45- // removes it from epoll, so ENOENT and EBADF are harmless here.
46- err := p.raw.Control(func(ep uintptr) {
47- for fd := range p.registered {
48- found := false
49- for _, f := range fds {
50- if int(f.Fd) == fd {
51- found = true
52- break
53- }
54- }
55- if !found {
56- unix.EpollCtl(int(ep), unix.EPOLL_CTL_DEL, fd, nil)
57- delete(p.registered, fd)
58- }
59- }
60- })
61- if err != nil {
62- return 0, err
63- }
64 var ctlErr error44 var ctlErr error
65- err = p.raw.Control(func(ep uintptr) {45+ added := 0
46+ err := p.raw.Control(func(ep uintptr) {
66 for _, f := range fds {47 for _, f := range fds {
67- fd := int(f.Fd)48+ if f.Fd < 0 {
68- if fd < 0 {49+ added++
69 continue50 continue
70 }51 }
71- // MOD detects a descriptor number recycled after its old file closed.52+ ev := unix.EpollEvent{Events: unix.EPOLLIN, Fd: f.Fd}
72- ev := unix.EpollEvent{Events: unix.EPOLLIN, Fd: int32(fd)}53+ if e := unix.EpollCtl(int(ep), unix.EPOLL_CTL_ADD, int(f.Fd), &ev); e != nil {
73- e := unix.EpollCtl(int(ep), unix.EPOLL_CTL_MOD, fd, &ev)
74- if errors.Is(e, unix.ENOENT) {
75- e = unix.EpollCtl(int(ep), unix.EPOLL_CTL_ADD, fd, &ev)
76- }
77- if e != nil {
78 ctlErr = e54 ctlErr = e
79 return55 return
80 }56 }
81- p.registered[fd] = struct{}{}57+ added++
58+ }
59+ })
60+ defer p.raw.Control(func(ep uintptr) {
61+ for _, f := range fds[:added] {
62+ if f.Fd >= 0 {
63+ unix.EpollCtl(int(ep), unix.EPOLL_CTL_DEL, int(f.Fd), nil)
64+ }
82 }65 }
83 })66 })
84 if err != nil {67 if err != nil {
M internal/adapters/fdwait/poller_test.go +7 -2
@@ -52,8 +52,13 @@ func TestPollReadinessTimeoutAndReplacement(t *testing.T) {
5252 if n, err := p.Poll(fds, 1000); n != 1 || err != nil {
5353 t.Fatalf("replacement: %d %v", n, err)
5454 }
55- if _, ok := p.registered[fd]; ok {
56- t.Fatal("old registration retained")
55+ if err := p.raw.Control(func(ep uintptr) {
56+ var events [1]unix.EpollEvent
57+ if n, err := unix.EpollWait(int(ep), events[:], 0); n != 0 || err != nil {
58+ t.Errorf("registration retained after Poll returned: %d %v", n, err)
59+ }
60+ }); err != nil {
61+ t.Fatal(err)
5762 }
5863 }
5964
@@ -52,8 +52,13 @@ func TestPollReadinessTimeoutAndReplacement(t *testing.T) {
52 if n, err := p.Poll(fds, 1000); n != 1 || err != nil {52 if n, err := p.Poll(fds, 1000); n != 1 || err != nil {
53 t.Fatalf("replacement: %d %v", n, err)53 t.Fatalf("replacement: %d %v", n, err)
54 }54 }
55- if _, ok := p.registered[fd]; ok {55+ if err := p.raw.Control(func(ep uintptr) {
56- t.Fatal("old registration retained")56+ var events [1]unix.EpollEvent
57+ if n, err := unix.EpollWait(int(ep), events[:], 0); n != 0 || err != nil {
58+ t.Errorf("registration retained after Poll returned: %d %v", n, err)
59+ }
60+ }); err != nil {
61+ t.Fatal(err)
57 }62 }
58 }63 }
59 64

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