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.

       -t THREADS, --threads THREADS
              Specifies the maximum number of threads to trace. default 65536.  Note. 40 bytes per thread.

       -e EDGES, --edges EDGES
              Specifies the maximum number of edge cases that can be recorded. default 65536. Note. 88 bytes per
              edge case.

       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

USER COMMANDS                                      2017-02-01                                        deadlock(8)