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arm64: percpu: rewrite ll/sc loops in assembly 

Writing the outer loop of an LL/SC sequence using do {...} while
constructs potentially allows the compiler to hoist memory accesses
between the STXR and the branch back to the LDXR. On CPUs that do not
guarantee forward progress of LL/SC loops when faced with memory
accesses to the same ERG (up to 2k) between the failed STXR and the
branch back, we may end up livelocking.

This patch avoids this issue in our percpu atomics by rewriting the
outer loop as part of the LL/SC inline assembly block.

Cc: <stable@vger.kernel.org>
Fixes: f97fc81079 ("arm64: percpu: Implement this_cpu operations")
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2016-07-04 17:44:48 +01:00
Родитель 1c5b51dfb7
Коммит 1e6e57d9b3
1 изменённых файлов: 56 добавлений и 64 удалений
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120
arch/arm64/include/asm/percpu.h
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@ -44,48 +44,44 @@ static inline unsigned long __percpu_##op(void *ptr, \
\
switch (size) { \
case 1: \
do { \
asm ("//__per_cpu_" #op "_1\n" \
"ldxrb %w[ret], %[ptr]\n" \
asm ("//__per_cpu_" #op "_1\n" \
"1: ldxrb %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
"stxrb %w[loop], %w[ret], %[ptr]\n" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u8 *)ptr) \
: [val] "Ir" (val)); \
} while (loop); \
" stxrb %w[loop], %w[ret], %[ptr]\n" \
" cbnz %w[loop], 1b" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u8 *)ptr) \
: [val] "Ir" (val)); \
break; \
case 2: \
do { \
asm ("//__per_cpu_" #op "_2\n" \
"ldxrh %w[ret], %[ptr]\n" \
asm ("//__per_cpu_" #op "_2\n" \
"1: ldxrh %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
"stxrh %w[loop], %w[ret], %[ptr]\n" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u16 *)ptr) \
: [val] "Ir" (val)); \
} while (loop); \
" stxrh %w[loop], %w[ret], %[ptr]\n" \
" cbnz %w[loop], 1b" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u16 *)ptr) \
: [val] "Ir" (val)); \
break; \
case 4: \
do { \
asm ("//__per_cpu_" #op "_4\n" \
"ldxr %w[ret], %[ptr]\n" \
asm ("//__per_cpu_" #op "_4\n" \
"1: ldxr %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
"stxr %w[loop], %w[ret], %[ptr]\n" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u32 *)ptr) \
: [val] "Ir" (val)); \
} while (loop); \
" stxr %w[loop], %w[ret], %[ptr]\n" \
" cbnz %w[loop], 1b" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u32 *)ptr) \
: [val] "Ir" (val)); \
break; \
case 8: \
do { \
asm ("//__per_cpu_" #op "_8\n" \
"ldxr %[ret], %[ptr]\n" \
asm ("//__per_cpu_" #op "_8\n" \
"1: ldxr %[ret], %[ptr]\n" \
#asm_op " %[ret], %[ret], %[val]\n" \
"stxr %w[loop], %[ret], %[ptr]\n" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u64 *)ptr) \
: [val] "Ir" (val)); \
} while (loop); \
" stxr %w[loop], %[ret], %[ptr]\n" \
" cbnz %w[loop], 1b" \
: [loop] "=&r" (loop), [ret] "=&r" (ret), \
[ptr] "+Q"(*(u64 *)ptr) \
: [val] "Ir" (val)); \
break; \
default: \
BUILD_BUG(); \
@ -150,44 +146,40 @@ static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
switch (size) {
case 1:
do {
asm ("//__percpu_xchg_1\n"
"ldxrb %w[ret], %[ptr]\n"
"stxrb %w[loop], %w[val], %[ptr]\n"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u8 *)ptr)
: [val] "r" (val));
} while (loop);
asm ("//__percpu_xchg_1\n"
"1: ldxrb %w[ret], %[ptr]\n"
" stxrb %w[loop], %w[val], %[ptr]\n"
" cbnz %w[loop], 1b"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u8 *)ptr)
: [val] "r" (val));
break;
case 2:
do {
asm ("//__percpu_xchg_2\n"
"ldxrh %w[ret], %[ptr]\n"
"stxrh %w[loop], %w[val], %[ptr]\n"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u16 *)ptr)
: [val] "r" (val));
} while (loop);
asm ("//__percpu_xchg_2\n"
"1: ldxrh %w[ret], %[ptr]\n"
" stxrh %w[loop], %w[val], %[ptr]\n"
" cbnz %w[loop], 1b"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u16 *)ptr)
: [val] "r" (val));
break;
case 4:
do {
asm ("//__percpu_xchg_4\n"
"ldxr %w[ret], %[ptr]\n"
"stxr %w[loop], %w[val], %[ptr]\n"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u32 *)ptr)
: [val] "r" (val));
} while (loop);
asm ("//__percpu_xchg_4\n"
"1: ldxr %w[ret], %[ptr]\n"
" stxr %w[loop], %w[val], %[ptr]\n"
" cbnz %w[loop], 1b"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u32 *)ptr)
: [val] "r" (val));
break;
case 8:
do {
asm ("//__percpu_xchg_8\n"
"ldxr %[ret], %[ptr]\n"
"stxr %w[loop], %[val], %[ptr]\n"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u64 *)ptr)
: [val] "r" (val));
} while (loop);
asm ("//__percpu_xchg_8\n"
"1: ldxr %[ret], %[ptr]\n"
" stxr %w[loop], %[val], %[ptr]\n"
" cbnz %w[loop], 1b"
: [loop] "=&r"(loop), [ret] "=&r"(ret),
[ptr] "+Q"(*(u64 *)ptr)
: [val] "r" (val));
break;
default:
BUILD_BUG();