Hello.
I hit kmemcheck splat on commit 49d31c2f389acfe8 ("dentry name snapshots") using linux-next-20170901.
Changing to strncpy() fixes this problem, but using strncpy() only if CONFIG_KMEMCHECK=y is better
for performance?
[ 788.180175] WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (ffff8fa27465ac50)
[ 788.184248] 636f6e66696766732e746d70000000000010000000000000020000000188ffff
[ 788.186989] i i i i i i i i i i i i i u u u u u u u u u u i i i i i u u u u
[ 788.189841] ^
[ 788.191937] RIP: 0010:take_dentry_name_snapshot+0x28/0x50
[ 788.194225] RSP: 0018:ffffa83000f5bdf8 EFLAGS: 00010246
[ 788.196453] RAX: 0000000000000020 RBX: ffff8fa274b20550 RCX: 0000000000000002
[ 788.199200] RDX: ffffa83000f5be40 RSI: ffff8fa27465ac50 RDI: ffffa83000f5be60
[ 788.201950] RBP: ffffa83000f5bdf8 R08: ffffa83000f5be48 R09: 0000000000000001
[ 788.204773] R10: ffff8fa27465ac00 R11: ffff8fa27465acc0 R12: ffff8fa27465ac00
[ 788.207625] R13: ffff8fa27465acc0 R14: 0000000000000000 R15: 0000000000000000
[ 788.210399] FS: 00007f79737ac8c0(0000) GS:ffffffff8fc30000(0000) knlGS:0000000000000000
[ 788.213422] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 788.215811] CR2: ffff8fa274c0b000 CR3: 0000000134aa7002 CR4: 00000000000606f0
[ 788.218679] take_dentry_name_snapshot+0x28/0x50
[ 788.220915] vfs_rename+0x128/0x870
[ 788.222765] SyS_rename+0x3b2/0x3d0
[ 788.224549] entry_SYSCALL_64_fastpath+0x1a/0xa4
[ 788.226645] 0xffffffffffffffff
# ./scripts/faddr2line vmlinux take_dentry_name_snapshot+0x28/0x50
take_dentry_name_snapshot+0x28/0x50:
__inline_memcpy at arch/x86/include/asm/string_64.h:13
(inlined by) take_dentry_name_snapshot at fs/dcache.c:294
0000000000000330 <take_dentry_name_snapshot>:
330: 55 push %rbp
331: 48 89 fa mov %rdi,%rdx
334: 48 89 e5 mov %rsp,%rbp
337: 48 8b 46 28 mov 0x28(%rsi),%rax
33b: 48 83 c6 38 add $0x38,%rsi
33f: 48 39 f0 cmp %rsi,%rax
342: 75 26 jne 36a <take_dentry_name_snapshot+0x3a>
344: 4c 8d 47 08 lea 0x8(%rdi),%r8
348: 48 89 c6 mov %rax,%rsi
34b: b9 08 00 00 00 mov $0x8,%ecx
350: b8 20 00 00 00 mov $0x20,%eax
355: 4c 89 c7 mov %r8,%rdi
358: f3 a5 rep movsl %ds:(%rsi),%es:(%rdi) // <= take_dentry_name_snapshot+0x28/0x50
35a: a8 02 test $0x2,%al
35c: 74 02 je 360 <take_dentry_name_snapshot+0x30>
35e: 66 a5 movsw %ds:(%rsi),%es:(%rdi)
360: a8 01 test $0x1,%al
362: 74 01 je 365 <take_dentry_name_snapshot+0x35>
364: a4 movsb %ds:(%rsi),%es:(%rdi)
365: 4c 89 02 mov %r8,(%rdx)
368: 5d pop %rbp
369: c3 retq
36a: ff 40 f0 incl -0x10(%rax)
36d: 48 89 07 mov %rax,(%rdi)
370: 5d pop %rbp
371: c3 retq
372: 0f 1f 40 00 nopl 0x0(%rax)
376: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
37d: 00 00 00
