Hello,
Can someone help me to understand why there is a potential data race
here?
Access to the data structure is protected by a mutex, and the error
message seems to even report that. So why is this a potential race?
==9352== ----------------------------------------------------------------
==9352==
==9352== Lock at 0x634AF38 was first observed
==9352== at 0x4C3010C: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x11A142: __gthread_mutex_lock (gthr-default.h:748)
==9352== by 0x11A142: std::mutex::lock() (std_mutex.h:103)
==9352== by 0x116E14: lock_guard (std_mutex.h:162)
==9352== by 0x116E14: sfs_do_readdir(fuse_req*, unsigned long, unsigned
long, long, fuse_file_info*, int) (steamfs.cpp:916)
==9352== by 0x4E51259: do_readdirplus (fuse_lowlevel.c:1469)
==9352== by 0x4E53C20: fuse_session_process_buf_int (fuse_lowlevel.c:2555)
==9352== by 0x4E4F980: fuse_do_work (fuse_loop_mt.c:160)
==9352== by 0x4C32D06: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x507E493: start_thread (pthread_create.c:333)
==9352== by 0x5915ACE: clone (clone.S:97)
==9352== Address 0x634af38 is 24 bytes inside a block of size 64 alloc'd
==9352== at 0x4C2D8CF: operator new(unsigned long, std::nothrow_t const&)
(in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x1146D0: sfs_opendir(fuse_req*, unsigned long, fuse_file_info*)
(steamfs.cpp:864)
==9352== by 0x4E52D0B: do_opendir (fuse_lowlevel.c:1441)
==9352== by 0x4E53C20: fuse_session_process_buf_int (fuse_lowlevel.c:2555)
==9352== by 0x4E4F980: fuse_do_work (fuse_loop_mt.c:160)
==9352== by 0x4C32D06: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x507E493: start_thread (pthread_create.c:333)
==9352== by 0x5915ACE: clone (clone.S:97)
==9352== Block was alloc'd by thread #3
==9352==
==9352== Possible data race during read of size 8 at 0x634AF30 by thread #5
==9352== Locks held: 1, at address 0x634AF38
==9352== at 0x116E15: sfs_do_readdir(fuse_req*, unsigned long, unsigned
long, long, fuse_file_info*, int) (steamfs.cpp:917)
==9352== by 0x4E51259: do_readdirplus (fuse_lowlevel.c:1469)
==9352== by 0x4E53C20: fuse_session_process_buf_int (fuse_lowlevel.c:2555)
==9352== by 0x4E4F980: fuse_do_work (fuse_loop_mt.c:160)
==9352== by 0x4C32D06: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x507E493: start_thread (pthread_create.c:333)
==9352== by 0x5915ACE: clone (clone.S:97)
==9352==
==9352== This conflicts with a previous write of size 8 by thread #3
==9352== Locks held: 1, at address 0x634AF38
==9352== at 0x116E81: sfs_do_readdir(fuse_req*, unsigned long, unsigned
long, long, fuse_file_info*, int) (steamfs.cpp:938)
==9352== by 0x4E51259: do_readdirplus (fuse_lowlevel.c:1469)
==9352== by 0x4E53C20: fuse_session_process_buf_int (fuse_lowlevel.c:2555)
==9352== by 0x4E4F980: fuse_do_work (fuse_loop_mt.c:160)
==9352== by 0x4C32D06: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x507E493: start_thread (pthread_create.c:333)
==9352== by 0x5915ACE: clone (clone.S:97)
==9352== Address 0x634af30 is 16 bytes inside a block of size 64 alloc'd
==9352== at 0x4C2D8CF: operator new(unsigned long, std::nothrow_t const&)
(in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x1146D0: sfs_opendir(fuse_req*, unsigned long, fuse_file_info*)
(steamfs.cpp:864)
==9352== by 0x4E52D0B: do_opendir (fuse_lowlevel.c:1441)
==9352== by 0x4E53C20: fuse_session_process_buf_int (fuse_lowlevel.c:2555)
==9352== by 0x4E4F980: fuse_do_work (fuse_loop_mt.c:160)
==9352== by 0x4C32D06: ??? (in
/usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==9352== by 0x507E493: start_thread (pthread_create.c:333)
==9352== by 0x5915ACE: clone (clone.S:97)
==9352== Block was alloc'd by thread #3
==9352==
==9352== ----------------------------------------------------------------
Best,
-Nikolaus
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