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author | Keir Fraser <keir.fraser@citrix.com> | 2010-07-05 08:24:18 +0100 |
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committer | Keir Fraser <keir.fraser@citrix.com> | 2010-07-05 08:24:18 +0100 |
commit | 712b05770c8dd3673310188f30616b7f6a3a1b22 (patch) | |
tree | 37d9e30fc824561f1083214253722bf4c1afe64d /xen/common/trace.c | |
parent | 2604adda4f817c3d9bf81a9c45b2bafda79ec4e9 (diff) | |
download | xen-712b05770c8dd3673310188f30616b7f6a3a1b22.tar.gz xen-712b05770c8dd3673310188f30616b7f6a3a1b22.tar.bz2 xen-712b05770c8dd3673310188f30616b7f6a3a1b22.zip |
trace: insert compiler memory barriers
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@novell.com>
Diffstat (limited to 'xen/common/trace.c')
-rw-r--r-- | xen/common/trace.c | 38 |
1 files changed, 20 insertions, 18 deletions
diff --git a/xen/common/trace.c b/xen/common/trace.c index 85554cd769..af2f46ed45 100644 --- a/xen/common/trace.c +++ b/xen/common/trace.c @@ -459,11 +459,13 @@ static inline bool_t bogus(u32 prod, u32 cons) 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; @@ -475,12 +477,14 @@ static inline u32 calc_unconsumed_bytes(const struct t_buf *buf) 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; @@ -495,11 +499,14 @@ static inline u32 calc_bytes_avail(const struct t_buf *buf) 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 ) @@ -526,23 +533,21 @@ static inline void __insert_record(struct t_buf *buf, 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; @@ -559,9 +564,6 @@ static inline void __insert_record(struct t_buf *buf, wmb(); - next = buf->prod; - if ( bogus(next, buf->cons) ) - return; next += rec_size; if ( next >= 2*data_size ) next -= 2*data_size; |