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sched/x86: Add stack frame dependency to __preempt_schedule[_notrace]()
If __preempt_schedule() or __preempt_schedule_notrace() is referenced at the beginning of a function, gcc can insert the asm inline "call ___preempt_schedule[_notrace]" instruction before setting up a stack frame, which breaks frame pointer convention if CONFIG_FRAME_POINTER is enabled and can result in bad stack traces. Force a stack frame to be created if CONFIG_FRAME_POINTER is enabled by listing the stack pointer as an output operand for the inline asm statements. Specifically this fixes the following stacktool warnings: stacktool: drivers/scsi/hpsa.o: hpsa_scsi_do_simple_cmd.constprop.106()+0x79: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_find_first()+0x70: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_find_first()+0x92: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_free()+0xff: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_free()+0xf5: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_free()+0x11a: call without frame pointer save/setup stacktool: fs/mbcache.o: mb_cache_entry_get()+0x225: call without frame pointer save/setup stacktool: kernel/locking/percpu-rwsem.o: percpu_up_read()+0x27: call without frame pointer save/setup stacktool: kernel/profile.o: do_profile_hits.isra.5()+0x139: call without frame pointer save/setup stacktool: lib/nmi_backtrace.o: nmi_trigger_all_cpu_backtrace()+0x2b6: call without frame pointer save/setup stacktool: net/rds/ib_cm.o: rds_ib_cq_comp_handler_recv()+0x58: call without frame pointer save/setup stacktool: net/rds/ib_cm.o: rds_ib_cq_comp_handler_send()+0x58: call without frame pointer save/setup stacktool: net/rds/ib_recv.o: rds_ib_attempt_ack()+0xc1: call without frame pointer save/setup stacktool: net/rds/iw_recv.o: rds_iw_attempt_ack()+0xc1: call without frame pointer save/setup stacktool: net/rds/iw_recv.o: rds_iw_recv_cq_comp_handler()+0x55: call without frame pointer save/setup So it only adds a stack frame to 15 call sites out of ~5000 calls to ___preempt_schedule[_notrace](). All the others already had stack frames. Oddly, this change actually seems to make things faster in a lot of cases. For many smaller functions it causes the stack frame creation to get moved out of the common path and into the unlikely path. For example, here's the original cyc2ns_read_end(): ffffffff8101f8c0 <cyc2ns_read_end>: ffffffff8101f8c0: 55 push %rbp ffffffff8101f8c1: 48 89 e5 mov %rsp,%rbp ffffffff8101f8c4: 83 6f 10 01 subl $0x1,0x10(%rdi) ffffffff8101f8c8: 75 08 jne ffffffff8101f8d2 <cyc2ns_read_end+0x12> ffffffff8101f8ca: 65 48 89 3d e6 5a ff mov %rdi,%gs:0x7eff5ae6(%rip) # 153b8 <cyc2ns+0x38> ffffffff8101f8d1: 7e ffffffff8101f8d2: 65 ff 0d 77 c4 fe 7e decl %gs:0x7efec477(%rip) # bd50 <__preempt_count> ffffffff8101f8d9: 74 02 je ffffffff8101f8dd <cyc2ns_read_end+0x1d> ffffffff8101f8db: 5d pop %rbp ffffffff8101f8dc: c3 retq ffffffff8101f8dd: e8 1e 37 fe ff callq ffffffff81003000 <___preempt_schedule> ffffffff8101f8e2: 5d pop %rbp ffffffff8101f8e3: c3 retq ffffffff8101f8e4: 66 66 66 2e 0f 1f 84 data16 data16 nopw %cs:0x0(%rax,%rax,1) ffffffff8101f8eb: 00 00 00 00 00 And here's the same function with the patch: ffffffff8101f8c0 <cyc2ns_read_end>: ffffffff8101f8c0: 83 6f 10 01 subl $0x1,0x10(%rdi) ffffffff8101f8c4: 75 08 jne ffffffff8101f8ce <cyc2ns_read_end+0xe> ffffffff8101f8c6: 65 48 89 3d ea 5a ff mov %rdi,%gs:0x7eff5aea(%rip) # 153b8 <cyc2ns+0x38> ffffffff8101f8cd: 7e ffffffff8101f8ce: 65 ff 0d 7b c4 fe 7e decl %gs:0x7efec47b(%rip) # bd50 <__preempt_count> ffffffff8101f8d5: 74 01 je ffffffff8101f8d8 <cyc2ns_read_end+0x18> ffffffff8101f8d7: c3 retq ffffffff8101f8d8: 55 push %rbp ffffffff8101f8d9: 48 89 e5 mov %rsp,%rbp ffffffff8101f8dc: e8 1f 37 fe ff callq ffffffff81003000 <___preempt_schedule> ffffffff8101f8e1: 5d pop %rbp ffffffff8101f8e2: c3 retq ffffffff8101f8e3: 66 66 66 66 2e 0f 1f data16 data16 data16 nopw %cs:0x0(%rax,%rax,1) ffffffff8101f8ea: 84 00 00 00 00 00 Notice that it moved the frame pointer setup code to the unlikely ___preempt_schedule() call path. Going through a sampling of the differences in the asm, that's the most common change I see. Otherwise it has no real effect on callers which already have stack frames (though it does result in the reordering of some 'mov's). Reported-by: Jiri Slaby <jslaby@suse.cz> Tested-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: live-patching@vger.kernel.org Link: http://lkml.kernel.org/r/20160218174158.GA28230@treble.redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -94,10 +94,19 @@ static __always_inline bool should_resched(int preempt_offset)
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#ifdef CONFIG_PREEMPT
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extern asmlinkage void ___preempt_schedule(void);
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# define __preempt_schedule() asm ("call ___preempt_schedule")
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# define __preempt_schedule() \
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({ \
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register void *__sp asm(_ASM_SP); \
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asm volatile ("call ___preempt_schedule" : "+r"(__sp)); \
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})
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extern asmlinkage void preempt_schedule(void);
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extern asmlinkage void ___preempt_schedule_notrace(void);
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# define __preempt_schedule_notrace() asm ("call ___preempt_schedule_notrace")
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# define __preempt_schedule_notrace() \
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({ \
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register void *__sp asm(_ASM_SP); \
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asm volatile ("call ___preempt_schedule_notrace" : "+r"(__sp)); \
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})
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extern asmlinkage void preempt_schedule_notrace(void);
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#endif
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