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

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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    5ee8dbf54602 Merge tag 'fsverity-for-linus' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101d5b5a580000
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
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11b888ba580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f758d6580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-5ee8dbf5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3cd4daffdac9/vmlinux-5ee8dbf5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7a6fec327094/bzImage-5ee8dbf5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+196a82fd904572696b3c@syzkaller.appspotmail.com

R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007ff784215fac R14: 00007ff784215fa0 R15: 00007ff784215fa0
 </TASK>
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.17/5460 is trying to acquire lock:
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118

but task is already holding lock:
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x4b0 kernel/events/core.c:7453

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&event->mmap_mutex);
  lock(&event->mmap_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.0.17/5460:
 #0: ffff888011a94080 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
 #0: ffff888011a94080 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0 mm/util.c:579
 #1: ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
 #1: ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x4b0 kernel/events/core.c:7453

stack backtrace:
CPU: 0 UID: 0 PID: 5460 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x253f/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776
 refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118
 perf_mmap_close+0x953/0xf90 kernel/events/core.c:7064
 perf_mmap+0x418/0x4b0 kernel/events/core.c:7488
 vfs_mmap include/linux/fs.h:2070 [inline]
 mmap_file mm/internal.h:167 [inline]
 __mmap_new_file_vma mm/vma.c:2468 [inline]
 __mmap_new_vma mm/vma.c:2532 [inline]
 __mmap_region mm/vma.c:2759 [inline]
 mmap_region+0x18fe/0x2240 mm/vma.c:2837
 do_mmap+0xc39/0x10c0 mm/mmap.c:559
 vm_mmap_pgoff+0x2c9/0x4f0 mm/util.c:581
 ksys_mmap_pgoff+0x51e/0x760 mm/mmap.c:605
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff783f9c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeef4c8518 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007ff784215fa0 RCX: 00007ff783f9c799
RDX: 0000000001000008 RSI: 0000000000002000 RDI: 0000200000ffe000
RBP: 00007ffeef4c8580 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007ff784215fac R14: 00007ff784215fa0 R15: 00007ff784215fa0
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

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

[Tetsuo Handa]

Side effect of commit 77de62ad3de3 ("perf/core: Fix refcount bug and potential UAF in perf_mmap").

On 2026/03/07 15:53, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    5ee8dbf54602 Merge tag 'fsverity-for-linus' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=101d5b5a580000
> 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
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11b888ba580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f758d6580000

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

[Qing Wang]

#syz test

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1f5699b339ec..accf23545d78 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7485,9 +7485,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 		 */
 		ret = map_range(event->rb, vma);
 		if (ret)
-			perf_mmap_close(vma);
+			goto out_close;
 	}
 
+	return ret;
+out_close:
+	perf_mmap_close(vma);
 	return ret;
 }
 

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:

failed to copy syz-executor to VM: failed to run ["scp" "-P" "41992" "-F" "/dev/null" "-o" "UserKnownHostsFile=/dev/null" "-o" "IdentitiesOnly=yes" "-o" "BatchMode=yes" "-o" "StrictHostKeyChecking=no" "-o" "ConnectTimeout=10" "/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/bin/linux_amd64/syz-executor" "root@localhost:/syz-executor"]: exit status 1



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-build1130506223=/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/cc2iNFRL.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=130d03aa580000

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

[Qing Wang]

#syz test

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1f5699b339ec..e5ce03ce926d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7485,9 +7485,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 		 */
 		ret = map_range(event->rb, vma);
 		if (ret)
-			perf_mmap_close(vma);
+			goto out_close;
 	}
+	return 0;
 
+out_close:
+	perf_mmap_close(vma);
 	return ret;
 }
 

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