Manual: deadlock-bpfcc

deadlock(8)					   System Manager's Manual					 deadlock(8)

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 in‐
	      lined 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,cus‐
	      tom_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  slow‐
       down 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)