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authorSatyam Sharma <satyam@infradead.org>2007-08-15 20:39:25 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-08-18 12:54:44 -0400
commit62be90012c507b2bf1047eb2eaa1e9151f7172fe (patch)
treed759ebb219a74d9bfa951b191d794d90814b7b2c /include/asm-i386
parent06bfb7eb1535822a3338ffea9918e22215abed90 (diff)
i386: Fix a couple busy loops in mach_wakecpu.h:wait_for_init_deassert()
Use cpu_relax() in the busy loops, as atomic_read() doesn't automatically imply volatility for i386 and x86_64. x86_64 doesn't have this issue because it open-codes the while loop in smpboot.c:smp_callin() itself that already uses cpu_relax(). For i386, however, smpboot.c:smp_callin() calls wait_for_init_deassert() which is buggy for mach-default and mach-es7000 cases. [ I test-built a kernel -- smp_callin() itself got inlined in its only callsite, smpboot.c:start_secondary() -- and the relevant piece of code disassembles to the following: 0xc1019704 <start_secondary+12>: mov 0xc144c4c8,%eax 0xc1019709 <start_secondary+17>: test %eax,%eax 0xc101970b <start_secondary+19>: je 0xc1019709 <start_secondary+17> init_deasserted (at 0xc144c4c8) gets fetched into %eax only once and then we loop over the test of the stale value in the register only, so these look like real bugs to me. With the fix below, this becomes: 0xc1019706 <start_secondary+14>: pause 0xc1019708 <start_secondary+16>: cmpl $0x0,0xc144c4c8 0xc101970f <start_secondary+23>: je 0xc1019706 <start_secondary+14> which looks nice and healthy. ] Thanks to Heiko Carstens for noticing this. Signed-off-by: Satyam Sharma <satyam@infradead.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/asm-i386')
-rw-r--r--include/asm-i386/mach-default/mach_wakecpu.h3
-rw-r--r--include/asm-i386/mach-es7000/mach_wakecpu.h3
2 files changed, 4 insertions, 2 deletions
diff --git a/include/asm-i386/mach-default/mach_wakecpu.h b/include/asm-i386/mach-default/mach_wakecpu.h
index 673b85c9b273..3ebb17893aa5 100644
--- a/include/asm-i386/mach-default/mach_wakecpu.h
+++ b/include/asm-i386/mach-default/mach_wakecpu.h
@@ -15,7 +15,8 @@
15 15
16static inline void wait_for_init_deassert(atomic_t *deassert) 16static inline void wait_for_init_deassert(atomic_t *deassert)
17{ 17{
18 while (!atomic_read(deassert)); 18 while (!atomic_read(deassert))
19 cpu_relax();
19 return; 20 return;
20} 21}
21 22
diff --git a/include/asm-i386/mach-es7000/mach_wakecpu.h b/include/asm-i386/mach-es7000/mach_wakecpu.h
index efc903b73486..84ff58314501 100644
--- a/include/asm-i386/mach-es7000/mach_wakecpu.h
+++ b/include/asm-i386/mach-es7000/mach_wakecpu.h
@@ -31,7 +31,8 @@ wakeup_secondary_cpu(int phys_apicid, unsigned long start_eip)
31static inline void wait_for_init_deassert(atomic_t *deassert) 31static inline void wait_for_init_deassert(atomic_t *deassert)
32{ 32{
33#ifdef WAKE_SECONDARY_VIA_INIT 33#ifdef WAKE_SECONDARY_VIA_INIT
34 while (!atomic_read(deassert)); 34 while (!atomic_read(deassert))
35 cpu_relax();
35#endif 36#endif
36 return; 37 return;
37} 38}