The patch titled
i386: Fix a couple of busy loops in mach_wakecpu.h:wait_for_init_deassert()
has been added to the -mm tree. Its filename is
i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: i386: Fix a couple of busy loops in mach_wakecpu.h:wait_for_init_deassert()
From: Satyam Sharma <satyam@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/asm-i386/mach-default/mach_wakecpu.h | 3 ++-
include/asm-i386/mach-es7000/mach_wakecpu.h | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)
diff -puN include/asm-i386/mach-default/mach_wakecpu.h~i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert include/asm-i386/mach-default/mach_wakecpu.h
--- a/include/asm-i386/mach-default/mach_wakecpu.h~i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert
+++ a/include/asm-i386/mach-default/mach_wakecpu.h
@@ -15,7 +15,8 @@
static inline void wait_for_init_deassert(atomic_t *deassert)
{
- while (!atomic_read(deassert));
+ while (!atomic_read(deassert))
+ cpu_relax();
return;
}
diff -puN include/asm-i386/mach-es7000/mach_wakecpu.h~i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert include/asm-i386/mach-es7000/mach_wakecpu.h
--- a/include/asm-i386/mach-es7000/mach_wakecpu.h~i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert
+++ a/include/asm-i386/mach-es7000/mach_wakecpu.h
@@ -31,7 +31,8 @@ wakeup_secondary_cpu(int phys_apicid, un
static inline void wait_for_init_deassert(atomic_t *deassert)
{
#ifdef WAKE_SECONDARY_VIA_INIT
- while (!atomic_read(deassert));
+ while (!atomic_read(deassert))
+ cpu_relax();
#endif
return;
}
_
Patches currently in -mm which might be from satyam@xxxxxxxxxxxxx are
ia64-include-kconfigpreempt.patch
git-netdev-all.patch
git-net.patch
introduce-u16_max-and-u32_max.patch
use-mutex-instead-of-semaphore-in-the-onstream-scsi-tape-driver.patch
i386-fix-a-couple-of-busy-loops-in-mach_wakecpuhwait_for_init_deassert.patch
slub-slob-use-unlikely-for-kfreezero_or_null_ptr-check.patch
argv_split-allow-argv_split-to-handle-null-pointer-in-argcp-parameter-gracefully.patch
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