Re: [syzbot] [perf?] possible deadlock in refcount_dec_and_mutex_lock (2)

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

lost connection to test machine



syzkaller login: [   97.295165][    T9] cfg80211: failed to load regulatory.db
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0xaf000)
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x400000)
Warning: Permanently added '[localhost]:25860' (ED25519) to the list of known hosts.
2026/03/09 06:38:40 parsed 1 programs
[  114.832215][ T5312] cgroup: Unknown subsys name 'net'
[  114.886131][ T5312] cgroup: Unknown subsys name 'cpuset'
[  114.893161][ T5312] cgroup: Unknown subsys name 'rlimit'
[  143.365998][ T1314] ieee802154 phy0 wpan0: encryption failed: -22
[  143.369198][ T1314] ieee802154 phy1 wpan1: encryption failed: -22
[  166.421433][ T1009] ata1.00: NCQ disabled due to excessive errors
[  166.425080][ T1009] ata1.00: exception Emask 0x0 SAct 0x1004000 SErr 0x0 action 0x6 frozen
[  166.429465][ T1009] ata1.00: failed command: WRITE FPDMA QUEUED
[  166.433585][ T1009] ata1.00: cmd 61/78:70:2e:60:04/05:00:00:00:00/40 tag 14 ncq dma 716800 out
[  166.433585][ T1009]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[  166.443249][ T1009] ata1.00: status: { DRDY }
[  166.445372][ T1009] ata1.00: failed command: WRITE FPDMA QUEUED
[  166.448286][ T1009] ata1.00: cmd 61/00:c0:be:89:04/20:00:00:00:00/40 tag 24 ncq dma 4194304 ou
[  166.448286][ T1009]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[  166.458365][ T1009] ata1.00: status: { DRDY }
[  166.460620][ T1009] ata1: hard resetting link
[  166.785912][ T1009] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[  166.790793][ T1009] ata1.00: configured for UDMA/100
[  166.794045][ T1009] ata1: EH complete
qemu-system-x86_64: hw/ide/core.c:934: ide_dma_cb: Assertion `prep_size >= 0 && prep_size <= n * 512' failed.
Connection to localhost closed by remote host.


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1821029113=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at 41d8037d3362
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=41d8037d336239d16aac70cd8cd917b77068d00b -X github.com/google/syzkaller/prog.gitRevisionDate=20260306-090128"  ./sys/syz-sysgen | grep -q false || go install -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=41d8037d336239d16aac70cd8cd917b77068d00b -X github.com/google/syzkaller/prog.gitRevisionDate=20260306-090128"  ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=41d8037d336239d16aac70cd8cd917b77068d00b -X github.com/google/syzkaller/prog.gitRevisionDate=20260306-090128"  -o ./bin/linux_amd64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_amd64
g++ -o ./bin/linux_amd64/syz-executor executor/executor.cc \
	-m64 -O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_amd64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"41d8037d336239d16aac70cd8cd917b77068d00b\"
/usr/bin/ld: /tmp/ccmKTIy0.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x386): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
./tools/check-syzos.sh 2>/dev/null



Tested on:

commit:         1f318b96 Linux 7.0-rc3
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=c5c49ee0942d1cdb
dashboard link: https://syzkaller.appspot.com/bug?extid=196a82fd904572696b3c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16d178d6580000