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SubjectRe: kernel: tracepoints: add support for relative references
+++ Ard Biesheuvel [19/08/17 19:10 +0100]:
>To avoid the need for relocating absolute references to tracepoint
>structures at boot time when running relocatable kernels (which may
>take a disproportionate amount of space), add the option to emit
>these tables as relative references instead.
>
>Cc: Steven Rostedt <rostedt@goodmis.org>
>Cc: Ingo Molnar <mingo@redhat.com>
>Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Hi Ard,

While testing this patchset I ran into the following general protection
fault when removing a module with tracepoints:

# rmmod kvm
[ 25.279049] general protection fault: 0000 [#1] SMP
[ 25.279385] Modules linked in: kvm(-) irqbypass
[ 25.279829] CPU: 0 PID: 125 Comm: rmmod Not tainted 4.13.0-rc2+ #1
[ 25.280007] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014
[ 25.280315] task: ffff9697db7c0000 task.stack: ffffa907802dc000
[ 25.280624] RIP: 0010:tracepoint_module_notify+0xd5/0x1d0
[ 25.280782] RSP: 0018:ffffa907802dfe68 EFLAGS: 00000287
[ 25.280963] RAX: ffffffffc02b6fb0 RBX: ffff9697ddb33440 RCX: ffffffffc02b70f0
[ 25.281168] RDX: 000163cc00016410 RSI: ffff9697df21d860 RDI: ffff9697de001900
[ 25.281371] RBP: ffffa907802dfe88 R08: 000000000001d860 R09: ffffffff941692b4
[ 25.281543] R10: fffff0ec4076ccc0 R11: 0000000000000300 R12: ffffffffc02ce740
[ 25.281716] R13: 0000000000000002 R14: ffffffffc02ce740 R15: 0000000000000000
[ 25.281917] FS: 0000000000a6e880(0000) GS:ffff9697df200000(0000) knlGS:0000000000000000
[ 25.282107] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 25.282254] CR2: 00000000004adfc0 CR3: 000000001f838000 CR4: 00000000000006f0
[ 25.282517] Call Trace:
[ 25.283019] notifier_call_chain+0x4a/0x70
[ 25.283287] blocking_notifier_call_chain+0x43/0x60
[ 25.283422] SyS_delete_module+0x1b8/0x240
[ 25.283542] ? SyS_chdir+0xc4/0xe0
[ 25.283648] entry_SYSCALL_64_fastpath+0x1a/0xa5
[ 25.283863] RIP: 0033:0x4ba267
[ 25.283947] RSP: 002b:00007ffc3316bdf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000b0
[ 25.284134] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004ba267
[ 25.284310] RDX: 0000000000000000 RSI: 0000000000000880 RDI: 00007ffc3316be00
[ 25.284511] RBP: 00007ffc3316be40 R08: 0000000000000003 R09: 0000000000000000
[ 25.284699] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000637672
[ 25.284916] R13: 00007ffc3316c1b0 R14: 0000000000000000 R15: 0000000000000000
[ 25.285226] Code: 00 48 89 43 08 e8 9c b4 0d 00 49 8b 84 24 90 02 00 00 48 85 c0 74 28 41 8b 94 24 8c 02 00 00 48 8d 0c d0 48 39 c8 73 17 48 8b 10 <48> 83 7a 28 00 0f 85 e8 00 00 00 48 83 c0 08 48 39 c1 77 e9 48
[ 25.286199] RIP: tracepoint_module_notify+0xd5/0x1d0 RSP: ffffa907802dfe68
[ 25.286708] ---[ end trace 04f35cade1663177 ]---

The offending line is in tp_module_going_check_quiescent() (shown inlined):

(gdb) list *(tracepoint_module_notify+0xd5)
0xffffffff811692d5 is in tracepoint_module_notify (/home/jeyu/work/jeyu-linux/kernel/tracepoint.c:402).
397 struct tracepoint * const *iter;
398
399 if (!begin)
400 return;
401 for (iter = begin; iter < end; iter++)
402 WARN_ON_ONCE((*iter)->funcs);
403 }
404
405 static int tracepoint_module_coming(struct module *mod)
406 {

The relative reference calculations need to be done here too.

Thanks,

Jessica

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