Huge number of SIGURG eating up the CPU

[ttc0419]

Go version

go version go1.21.6 linux/amd64

Output of go env in your module/workspace:

default

What did you do?

strace the thread with high CPU usage
same program in #68414, but closed without any further response.

What did you see happen?

--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458944
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44457664
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875376
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 140016272782680
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875328
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875376
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458944
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458944
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875376
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458432
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875328
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824647875328
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458944
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44458432
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44457664
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 76824920
futex(0x4944158, FUTEX_WAKE_PRIVATE, 1) = 1
accept4(13, {sa_family=AF_INET6, sin6_port=htons(52040), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:10.88.4.4", &sin6_addr), sin6_scope_id=0}, [112->28], SOCK_CLOEXEC|SOCK_NONBLOCK) = 29
epoll_ctl(4, EPOLL_CTL_ADD, 29, {EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLET, {u32=2868905599, u64=9176106624710870655}}) = 0
getsockname(29, {sa_family=AF_INET6, sin6_port=htons(8080), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:10.88.8.60", &sin6_addr), sin6_scope_id=0}, [112->28]) = 0
setsockopt(29, SOL_TCP, TCP_NODELAY, [1], 4) = 0
setsockopt(29, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
setsockopt(29, SOL_TCP, TCP_KEEPINTVL, [15], 4) = 0
setsockopt(29, SOL_TCP, TCP_KEEPIDLE, [15], 4) = 0
accept4(13, {sa_family=AF_INET6, sin6_port=htons(52042), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:10.88.4.4", &sin6_addr), sin6_scope_id=0}, [112->28], SOCK_CLOEXEC|SOCK_NONBLOCK) = 30
epoll_ctl(4, EPOLL_CTL_ADD, 30, {EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLET, {u32=91226359, u64=9176106458724434167}}) = 0
getsockname(30, {sa_family=AF_INET6, sin6_port=htons(8080), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:10.88.8.60", &sin6_addr), sin6_scope_id=0}, [112->28]) = 0
setsockopt(30, SOL_TCP, TCP_NODELAY, [1], 4) = 0
setsockopt(30, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
setsockopt(30, SOL_TCP, TCP_KEEPINTVL, [15], 4) = 0
setsockopt(30, SOL_TCP, TCP_KEEPIDLE, [15], 4) = 0
accept4(13, 0xc0006e17e0, [112], SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
read(30, "GET /status HTTP/1.1\r\nHo", 24) = 24
read(30, "st: 10.88.8.60:8080\r\nUser-Agent:"..., 4094) = 85
write(30, "HTTP/1.1 200 OK\r\nVary: Origin\r\nD"..., 151) = 151
epoll_ctl(4, EPOLL_CTL_DEL, 30, 0xc0007ff93c) = 0
close(30)                               = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
read(29, "GET /status HTTP/1.1\r\nHo", 24) = 24
read(29, "st: 10.88.8.60:8080\r\nUser-Agent:"..., 4094) = 85
write(29, "HTTP/1.1 200 OK\r\nVary: Origin\r\nD"..., 151) = 151
epoll_ctl(4, EPOLL_CTL_DEL, 29, 0xc0007ff93c) = 0
close(29)                               = 0
epoll_pwait(4, [], 128, 0, NULL, 0)     = 0
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 1
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44457664
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 44457664
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824633982976
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 0
read(42, "\27\3\3\0\35\37g\2013Q\201V\374\321\364\202\337.\336\301\364P@[\264\365\207\31\\\213\22\272"..., 2688) = 34
read(42, 0xc000c14a80, 2688)            = -1 EAGAIN (Resource temporarily unavailable)
--- SIGURG {si_signo=SIGURG, si_code=SI_TKILL, si_pid=1, si_uid=0} ---
rt_sigreturn({mask=[]})                 = 824678144192

What did you expect to see?

less signals wasting CPU time?

[gabyhelp]

Related Issues and Documentation

• runtime: cgo stuck because of go signal handler went into dead loop #56649 (closed)
• A suspicious bug about panic #18431 (closed)
• runtime: gc goroutine occasionally use 100% CPU #61046
• runtime: SIGILL on s390x #15441 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

see #37942, I don't see anything about CPU time here

[ttc0419]

@seankhliao Please do not close the issue without any confirmation. If you need proof of something, ask and wait at least for some time and then close it. Anyway, here is your proof:

cut.mp4

[seankhliao]

as indicated by the other issue, sigurg is used by the runtime internally for preemption, if your application is stuck it is unlikely to be the cause, only a symptom.