Hi We are working on a dynamic data race detector for Linux kernel called KernelThreadSanitizer (ktsan) (https://code.google.com/p/thread-sanitizer/wiki/ThreadSanitizerForKernel). Here is a report we got while running ktsan (upstream revision fc14f9c1272f62c3e8d01300f52467c0d9af50f9, Linux 3.18-rc5): ================================================================== ThreadSanitizer: data-race in lockref_put_or_lock Read of size 8 by thread T575 (K814): [<ffffffff8152067f>] lockref_put_or_lock+0x1f/0xe0 /lib/lockref.c:122 [<ffffffff8126965e>] dput+0x2e/0x2b0 /fs/dcache.c:626 [< inlined >] link_path_walk+0xddd/0x1d40 path_to_nameidata /fs/namei.c:677 [< inlined >] link_path_walk+0xddd/0x1d40 walk_component /fs/namei.c:1571 [<ffffffff81257d7d>] link_path_walk+0xddd/0x1d40 /fs/namei.c:1805 [<ffffffff8125e344>] path_openat+0xe4/0xb10 /fs/namei.c:3206 [<ffffffff81260911>] do_filp_open+0x51/0xd0 /fs/namei.c:3259 [<ffffffff81242003>] do_sys_open+0x183/0x2d0 /fs/open.c:998 [< inlined >] SyS_open+0x35/0x50 SYSC_open /fs/open.c:1016 [<ffffffff81242185>] SyS_open+0x35/0x50 /fs/open.c:1011 [<ffffffff81e39fe9>] system_call_fastpath+0x12/0x17 /arch/x86/kernel/entry_64.S:422 DBG: cpu = ffffe8ffffc010b0 Previous write of size 4 by thread T574 (K813): [<ffffffff8126e22f>] __d_lookup+0x27f/0x2d0 /fs/dcache.c:2185 [<ffffffff812543c9>] lookup_fast+0x299/0x5a0 /fs/namei.c:1427 [< inlined >] link_path_walk+0x25c/0x1d40 walk_component /fs/namei.c:1546 [<ffffffff812571fc>] link_path_walk+0x25c/0x1d40 /fs/namei.c:1805 [<ffffffff8125e344>] path_openat+0xe4/0xb10 /fs/namei.c:3206 [<ffffffff81260911>] do_filp_open+0x51/0xd0 /fs/namei.c:3259 [<ffffffff81242003>] do_sys_open+0x183/0x2d0 /fs/open.c:998 [< inlined >] SyS_open+0x35/0x50 SYSC_open /fs/open.c:1016 [<ffffffff81242185>] SyS_open+0x35/0x50 /fs/open.c:1011 [<ffffffff81e39fe9>] system_call_fastpath+0x12/0x17 /arch/x86/kernel/entry_64.S:422 DBG: cpu = 0 DBG: addr: ffff8801148e91f0 DBG: first offset: 4, second offset: 0 DBG: T575 clock: {T575: 27630, T574: 25486} DBG: T574 clock: {T574: 25539} ================================================================== It seems that one thread increments 'dentry->d_lockref.count', while other does 'lockref_put_or_lock(&dentry->d_lockref)' without any synchronization. Could you confirm if this is a real race? Thank you. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
