ftrace: Clean up hash direct_functions on register failures
We see the following GPF when register_ftrace_direct fails:
[ ] general protection fault, probably for non-canonical address \
0x200000000000010: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI
[...]
[ ] RIP: 0010:ftrace_find_rec_direct+0x53/0x70
[ ] Code: 48 c1 e0 03 48 03 42 08 48 8b 10 31 c0 48 85 d2 74 [...]
[ ] RSP: 0018:
ffffc9000138bc10 EFLAGS:
00010206
[ ] RAX:
0000000000000000 RBX:
ffffffff813e0df0 RCX:
000000000000003b
[ ] RDX:
0200000000000000 RSI:
000000000000000c RDI:
ffffffff813e0df0
[ ] RBP:
ffffffffa00a3000 R08:
ffffffff81180ce0 R09:
0000000000000001
[ ] R10:
ffffc9000138bc18 R11:
0000000000000001 R12:
ffffffff813e0df0
[ ] R13:
ffffffff813e0df0 R14:
ffff888171b56400 R15:
0000000000000000
[ ] FS:
00007fa9420c7780(0000) GS:
ffff888ff6a00000(0000) knlGS:
000000000
[ ] CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[ ] CR2:
000000000770d000 CR3:
0000000107d50003 CR4:
0000000000370ee0
[ ] DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
[ ] DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
[ ] Call Trace:
[ ] <TASK>
[ ] register_ftrace_direct+0x54/0x290
[ ] ? render_sigset_t+0xa0/0xa0
[ ] bpf_trampoline_update+0x3f5/0x4a0
[ ] ? 0xffffffffa00a3000
[ ] bpf_trampoline_link_prog+0xa9/0x140
[ ] bpf_tracing_prog_attach+0x1dc/0x450
[ ] bpf_raw_tracepoint_open+0x9a/0x1e0
[ ] ? find_held_lock+0x2d/0x90
[ ] ? lock_release+0x150/0x430
[ ] __sys_bpf+0xbd6/0x2700
[ ] ? lock_is_held_type+0xd8/0x130
[ ] __x64_sys_bpf+0x1c/0x20
[ ] do_syscall_64+0x3a/0x80
[ ] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ ] RIP: 0033:0x7fa9421defa9
[ ] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 9 f8 [...]
[ ] RSP: 002b:
00007ffed743bd78 EFLAGS:
00000246 ORIG_RAX:
0000000000000141
[ ] RAX:
ffffffffffffffda RBX:
00000000069d2480 RCX:
00007fa9421defa9
[ ] RDX:
0000000000000078 RSI:
00007ffed743bd80 RDI:
0000000000000011
[ ] RBP:
00007ffed743be00 R08:
0000000000bb7270 R09:
0000000000000000
[ ] R10:
00000000069da210 R11:
0000000000000246 R12:
0000000000000001
[ ] R13:
00007ffed743c4b0 R14:
00000000069d2480 R15:
0000000000000001
[ ] </TASK>
[ ] Modules linked in: klp_vm(OK)
[ ] ---[ end trace
0000000000000000 ]---
One way to trigger this is:
1. load a livepatch that patches kernel function xxx;
2. run bpftrace -e 'kfunc:xxx {}', this will fail (expected for now);
3. repeat #2 => gpf.
This is because the entry is added to direct_functions, but not removed.
Fix this by remove the entry from direct_functions when
register_ftrace_direct fails.
Also remove the last trailing space from ftrace.c, so we don't have to
worry about it anymore.
Link: https://lkml.kernel.org/r/20220524170839.900849-1-song@kernel.org
Cc: stable@vger.kernel.org
Fixes: 763e34e74bb7 ("ftrace: Add register_ftrace_direct()")
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>