====================================================== WARNING: possible circular locking dependency detected 4.14.108+ #39 Not tainted ------------------------------------------------------ syz-executor.5/5787 is trying to acquire lock: (&sig->cred_guard_mutex){+.+.}, at: [] lock_trace+0x3f/0xc0 fs/proc/base.c:408 but task is already holding lock: (&p->lock){+.+.}, at: [] seq_read+0xcd/0x1180 fs/seq_file.c:165 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&p->lock){+.+.}: -> #1 (&pipe->mutex/1){+.+.}: -> #0 (&sig->cred_guard_mutex){+.+.}: other info that might help us debug this: Chain exists of: &sig->cred_guard_mutex --> &pipe->mutex/1 --> &p->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&p->lock); lock(&pipe->mutex/1); lock(&p->lock); lock(&sig->cred_guard_mutex); *** DEADLOCK *** 2 locks held by syz-executor.5/5787: #0: (sb_writers#7){.+.+}, at: [] file_start_write include/linux/fs.h:2726 [inline] #0: (sb_writers#7){.+.+}, at: [] do_sendfile+0x88f/0xb20 fs/read_write.c:1437 #1: (&p->lock){+.+.}, at: [] seq_read+0xcd/0x1180 fs/seq_file.c:165 stack backtrace: CPU: 1 PID: 5787 Comm: syz-executor.5 Not tainted 4.14.108+ #39 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xb9/0x10e lib/dump_stack.c:53 print_circular_bug.isra.0.cold+0x2dc/0x425 kernel/locking/lockdep.c:1258 SELinux: unrecognized netlink message: protocol=4 nlmsg_type=34982 sclass=netlink_tcpdiag_socket pig=5906 comm=syz-executor.2 SELinux: unrecognized netlink message: protocol=6 nlmsg_type=9617 sclass=netlink_xfrm_socket pig=6043 comm=syz-executor.2 SELinux: unrecognized netlink message: protocol=6 nlmsg_type=9617 sclass=netlink_xfrm_socket pig=6043 comm=syz-executor.2 netlink: 48 bytes leftover after parsing attributes in process `syz-executor.2'. netlink: 48 bytes leftover after parsing attributes in process `syz-executor.2'. ip6_tunnel: ip6tnl3 xmit: Local address not yet configured! netlink: 48 bytes leftover after parsing attributes in process `syz-executor.2'. netlink: 48 bytes leftover after parsing attributes in process `syz-executor.2'.