>>> On 05.07.10 at 10:06, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> I think I already applied this patch.
Indeed - I forgot to check the staging tree before sending, and
assumed you would be waiting for George's ack.
Jan
> On 05/07/2010 09:01, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>
>> This is to ensure fields shared writably with Dom0 get read only once
>> for any consistency checking followed by actual calculations.
>>
>> I realized there was another multiple-read issue, a fix for which is
>> also included (which at once simplifies __insert_record()).
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>>
>> --- a/xen/common/trace.c 2010-07-01 10:05:54.000000000 +0200
>> +++ b/xen/common/trace.c 2010-07-01 14:01:47.000000000 +0200
>> @@ -437,11 +437,13 @@ static inline bool_t bogus(u32 prod, u32
>> static inline u32 calc_unconsumed_bytes(const struct t_buf *buf)
>> {
>> u32 prod = buf->prod, cons = buf->cons;
>> - s32 x = prod - cons;
>> + s32 x;
>>
>> + barrier(); /* must read buf->prod and buf->cons only once */
>> if ( bogus(prod, cons) )
>> return data_size;
>>
>> + x = prod - cons;
>> if ( x < 0 )
>> x += 2*data_size;
>>
>> @@ -453,12 +455,14 @@ static inline u32 calc_unconsumed_bytes(
>>
>> static inline u32 calc_bytes_to_wrap(const struct t_buf *buf)
>> {
>> - u32 prod = buf->prod;
>> - s32 x = data_size - prod;
>> + u32 prod = buf->prod, cons = buf->cons;
>> + s32 x;
>>
>> - if ( bogus(prod, buf->cons) )
>> + barrier(); /* must read buf->prod and buf->cons only once */
>> + if ( bogus(prod, cons) )
>> return 0;
>>
>> + x = data_size - prod;
>> if ( x <= 0 )
>> x += data_size;
>>
>> @@ -473,11 +477,14 @@ static inline u32 calc_bytes_avail(const
>> return data_size - calc_unconsumed_bytes(buf);
>> }
>>
>> -static inline struct t_rec *next_record(const struct t_buf *buf)
>> +static inline struct t_rec *next_record(const struct t_buf *buf,
>> + uint32_t *next)
>> {
>> - u32 x = buf->prod;
>> + u32 x = buf->prod, cons = buf->cons;
>>
>> - if ( !tb_init_done || bogus(x, buf->cons) )
>> + barrier(); /* must read buf->prod and buf->cons only once */
>> + *next = x;
>> + if ( !tb_init_done || bogus(x, cons) )
>> return NULL;
>>
>> if ( x >= data_size )
>> @@ -504,23 +511,21 @@ static inline void __insert_record(volat
>> BUG_ON(local_rec_size != rec_size);
>> BUG_ON(extra & 3);
>>
>> + rec = next_record(buf, &next);
>> + if ( !rec )
>> + return;
>> /* Double-check once more that we have enough space.
>> * Don't bugcheck here, in case the userland tool is doing
>> * something stupid. */
>> - next = calc_bytes_avail(buf);
>> - if ( next < rec_size )
>> + if ( (unsigned char *)rec + rec_size > this_cpu(t_data) + data_size )
>> {
>> if ( printk_ratelimit() )
>> printk(XENLOG_WARNING
>> - "%s: avail=%u (size=%08x prod=%08x cons=%08x) rec=%u\n",
>> - __func__, next, data_size, buf->prod, buf->cons,
>> rec_size);
>> + "%s: size=%08x prod=%08x cons=%08x rec=%u\n",
>> + __func__, data_size, next, buf->cons, rec_size);
>> return;
>> }
>> - rmb();
>>
>> - rec = next_record(buf);
>> - if ( !rec )
>> - return;
>> rec->event = event;
>> rec->extra_u32 = extra_word;
>> dst = (unsigned char *)rec->u.nocycles.extra_u32;
>> @@ -537,9 +542,6 @@ static inline void __insert_record(volat
>>
>> wmb();
>>
>> - next = buf->prod;
>> - if ( bogus(next, buf->cons) )
>> - return;
>> next += rec_size;
>> if ( next >= 2*data_size )
>> next -= 2*data_size;
>>
>>
>>
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