NAME

       deadlock - Find potential deadlocks (lock order inversions) in a running program.

SYNOPSIS

       deadlock  [-h]  [--binary  BINARY]  [--dump-graph  DUMP_GRAPH] [--verbose] [--lock-symbols
       LOCK_SYMBOLS] [--unlock-symbols UNLOCK_SYMBOLS] pid

DESCRIPTION

       deadlock finds potential deadlocks in a running process. The program attaches  uprobes  on
       `pthread_mutex_lock`  and `pthread_mutex_unlock` by default to build a mutex wait directed
       graph, and then looks for a cycle in this graph.  This graph has the following properties:

       - Nodes in the graph represent mutexes.

       - Edge (A, B) exists if there exists some thread T where lock(A) was  called  and  lock(B)
       was called before unlock(A) was called.

       If  there  is  a  cycle in this graph, this indicates that there is a lock order inversion
       (potential deadlock). If the program finds a lock order inversion, the program  will  dump
       the cycle of mutexes, dump the stack traces where each mutex was acquired, and then exit.

       This program can only find potential deadlocks that occur while the program is tracing the
       process. It cannot find deadlocks that may have occurred before the program  was  attached
       to the process.

       This tool does not work for shared mutexes or recursive mutexes.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc

OPTIONS

       -h, --help
              show this help message and exit

       --binary BINARY
              If  set,  trace  the  mutexes  from  the binary at this path. For statically-linked
              binaries, this argument is not required.   For  dynamically-linked  binaries,  this
              argument  is  required  and should be the path of the pthread library the binary is
              using.  Example: /lib/x86_64-linux-gnu/libpthread.so.0

       --dump-graph DUMP_GRAPH
              If set, this will dump the mutex graph to the specified file.

       --verbose
              Print statistics about the mutex wait graph.

       --lock-symbols LOCK_SYMBOLS
              Comma-separated list of lock  symbols  to  trace.  Default  is  pthread_mutex_lock.
              These symbols cannot be inlined in the binary.

       --unlock-symbols UNLOCK_SYMBOLS
              Comma-separated  list  of unlock symbols to trace. Default is pthread_mutex_unlock.
              These symbols cannot be inlined in the binary.

       pid    Pid to trace

EXAMPLES

       Find potential deadlocks in PID 181. The --binary argument is not needed  for  statically-
       linked binaries.
              # deadlock 181

       Find  potential deadlocks in PID 181. If the process was created from a dynamically-linked
       executable, the --binary argument is required and must be the path of the pthread library:
              # deadlock 181 --binary /lib/x86_64-linux-gnu/libpthread.so.0

       Find potential deadlocks in PID 181. If the process was created from  a  statically-linked
       executable,  optionally  pass  the  location  of  the  binary.  On  older  kernels without
       https://lkml.org/lkml/2017/1/13/585, binaries that contain  `:`  in  the  path  cannot  be
       attached with uprobes. As a workaround, we can create a symlink to the binary, and provide
       the symlink name instead with the `--binary` option:
              # deadlock 181 --binary /usr/local/bin/lockinversion

       Find potential deadlocks in PID 181 and dump the mutex wait graph to a file:
              # deadlock 181 --dump-graph graph.json

       Find potential deadlocks in PID 181 and print mutex wait graph statistics:
              # deadlock 181 --verbose

       Find potential deadlocks in PID 181 with custom mutexes:
              #     deadlock     181     --lock-symbols     custom_mutex1_lock,custom_mutex2_lock
              --unlock_symbols custom_mutex1_unlock,custom_mutex2_unlock

OUTPUT

       This  program  does  not  output any fields. Rather, it will keep running until it finds a
       potential deadlock, or the user hits Ctrl-C. If the program finds a potential deadlock, it
       will output the stack traces and lock order inversion in the following format and exit:

       Potential Deadlock Detected!

       Cycle in lock order graph: Mutex M0 => Mutex M1 => Mutex M0

       Mutex M1 acquired here while holding Mutex M0 in Thread T:
              [stack trace]

       Mutex M0 previously acquired by the same Thread T here:
              [stack trace]

       Mutex M0 acquired here while holding Mutex M1 in Thread S:
              [stack trace]

       Mutex M1 previously acquired by the same Thread S here:
              [stack trace]

       Thread T created by Thread R here:
              [stack trace]

       Thread S created by Thread Q here:
              [stack trace]

OVERHEAD

       This  traces all mutex lock and unlock events and all thread creation events on the traced
       process. The overhead of this can be high if the process has many threads and mutexes. You
       should only run this on a process where the slowdown is acceptable.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also  look  in  the bcc distribution for a companion _examples.txt file containing example
       usage, output, and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Kenny Yu