From 24f3f6b5eff92608a62449e33bfac0eed1447d02 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Mon, 15 Nov 2010 09:18:49 -0500 Subject: arch/tile: fix rwlock so would-be write lockers don't block new readers This avoids a deadlock in the IGMP code where one core gets a read lock, another core starts trying to get a write lock (thus blocking new readers), and then the first core tries to recursively re-acquire the read lock. We still try to preserve some degree of balance by giving priority to additional write lockers that come along while the lock is held for write, so they can all complete quickly and return the lock to the readers. Signed-off-by: Chris Metcalf --- arch/tile/lib/spinlock_32.c | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) (limited to 'arch/tile') diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c index 485e24d62c6b..5cd1c4004eca 100644 --- a/arch/tile/lib/spinlock_32.c +++ b/arch/tile/lib/spinlock_32.c @@ -167,23 +167,30 @@ void arch_write_lock_slow(arch_rwlock_t *rwlock, u32 val) * when we compare them. */ u32 my_ticket_; + u32 iterations = 0; - /* Take out the next ticket; this will also stop would-be readers. */ - if (val & 1) - val = get_rwlock(rwlock); - rwlock->lock = __insn_addb(val, 1 << WR_NEXT_SHIFT); + /* + * Wait until there are no readers, then bump up the next + * field and capture the ticket value. + */ + for (;;) { + if (!(val & 1)) { + if ((val >> RD_COUNT_SHIFT) == 0) + break; + rwlock->lock = val; + } + delay_backoff(iterations++); + val = __insn_tns((int *)&rwlock->lock); + } - /* Extract my ticket value from the original word. */ + /* Take out the next ticket and extract my ticket value. */ + rwlock->lock = __insn_addb(val, 1 << WR_NEXT_SHIFT); my_ticket_ = val >> WR_NEXT_SHIFT; - /* - * Wait until the "current" field matches our ticket, and - * there are no remaining readers. - */ + /* Wait until the "current" field matches our ticket. */ for (;;) { u32 curr_ = val >> WR_CURR_SHIFT; - u32 readers = val >> RD_COUNT_SHIFT; - u32 delta = ((my_ticket_ - curr_) & WR_MASK) + !!readers; + u32 delta = ((my_ticket_ - curr_) & WR_MASK); if (likely(delta == 0)) break; -- cgit v1.2.3-58-ga151 From 4d658d13c90f14cf3510ca15cafe2f4aa9e23d64 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Wed, 24 Nov 2010 13:42:15 -0500 Subject: arch/tile: make glibc's sysconf(_SC_NPROCESSORS_CONF) work correctly glibc assumes that it can count /sys/devices/system/cpu/cpu* to get the number of configured cpus. For this to be valid on tile, we need to generate a "cpu" entry for all cpus, including the ones that are not currently allocated for Linux's use. Signed-off-by: Chris Metcalf --- arch/tile/kernel/setup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/tile') diff --git a/arch/tile/kernel/setup.c b/arch/tile/kernel/setup.c index fb0b3cbeae14..f18573643ed1 100644 --- a/arch/tile/kernel/setup.c +++ b/arch/tile/kernel/setup.c @@ -840,7 +840,7 @@ static int __init topology_init(void) for_each_online_node(i) register_one_node(i); - for_each_present_cpu(i) + for (i = 0; i < smp_height * smp_width; ++i) register_cpu(&cpu_devices[i], i); return 0; -- cgit v1.2.3-58-ga151 From 3edabee2ed22ee4f98f4b4bb38a41059226a8446 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Wed, 24 Nov 2010 13:57:42 -0500 Subject: arch/tile: fix memchr() not to dereference memory for zero length This change fixes a bug that memchr() will read the first word of the source even if the length is zero. Ironically, the code was originally written with a test to avoid exactly this problem, but to make the code conform to Linux coding standards with all declarations preceding all statements, the first load from memory was moved up above that test as the initial value for a variable. The change just moves all the variable declarations to the top of the file, with no initializers, so that the test can also be at the top of the file. Signed-off-by: Chris Metcalf --- arch/tile/lib/memchr_32.c | 35 +++++++++++++++++++---------------- 1 file changed, 19 insertions(+), 16 deletions(-) (limited to 'arch/tile') diff --git a/arch/tile/lib/memchr_32.c b/arch/tile/lib/memchr_32.c index 6235283b4859..cc3d9badf030 100644 --- a/arch/tile/lib/memchr_32.c +++ b/arch/tile/lib/memchr_32.c @@ -18,12 +18,24 @@ void *memchr(const void *s, int c, size_t n) { + const uint32_t *last_word_ptr; + const uint32_t *p; + const char *last_byte_ptr; + uintptr_t s_int; + uint32_t goal, before_mask, v, bits; + char *ret; + + if (__builtin_expect(n == 0, 0)) { + /* Don't dereference any memory if the array is empty. */ + return NULL; + } + /* Get an aligned pointer. */ - const uintptr_t s_int = (uintptr_t) s; - const uint32_t *p = (const uint32_t *)(s_int & -4); + s_int = (uintptr_t) s; + p = (const uint32_t *)(s_int & -4); /* Create four copies of the byte for which we are looking. */ - const uint32_t goal = 0x01010101 * (uint8_t) c; + goal = 0x01010101 * (uint8_t) c; /* Read the first word, but munge it so that bytes before the array * will not match goal. @@ -31,23 +43,14 @@ void *memchr(const void *s, int c, size_t n) * Note that this shift count expression works because we know * shift counts are taken mod 32. */ - const uint32_t before_mask = (1 << (s_int << 3)) - 1; - uint32_t v = (*p | before_mask) ^ (goal & before_mask); + before_mask = (1 << (s_int << 3)) - 1; + v = (*p | before_mask) ^ (goal & before_mask); /* Compute the address of the last byte. */ - const char *const last_byte_ptr = (const char *)s + n - 1; + last_byte_ptr = (const char *)s + n - 1; /* Compute the address of the word containing the last byte. */ - const uint32_t *const last_word_ptr = - (const uint32_t *)((uintptr_t) last_byte_ptr & -4); - - uint32_t bits; - char *ret; - - if (__builtin_expect(n == 0, 0)) { - /* Don't dereference any memory if the array is empty. */ - return NULL; - } + last_word_ptr = (const uint32_t *)((uintptr_t) last_byte_ptr & -4); while ((bits = __insn_seqb(v, goal)) == 0) { if (__builtin_expect(p == last_word_ptr, 0)) { -- cgit v1.2.3-58-ga151