X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=lib%2Fringbuffer%2Fring_buffer_frontend.c;h=38dbb937462d3140365b6cb22599d9de24a083c6;hb=d78fe19d2fd65bf438cbcf9ef362c4803a71fedf;hp=dc0357f56a3e71547c7da80a4e2bd3ce7277d0f0;hpb=886d51a3d7ed5fa6b41d7f19b3e14ae6c535a44c;p=lttng-modules.git diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c index dc0357f5..38dbb937 100644 --- a/lib/ringbuffer/ring_buffer_frontend.c +++ b/lib/ringbuffer/ring_buffer_frontend.c @@ -402,7 +402,7 @@ static void lib_ring_buffer_stop_read_timer(struct lib_ring_buffer *buf) * Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD) */ static -int __cpuinit lib_ring_buffer_cpu_hp_callback(struct notifier_block *nb, +int lib_ring_buffer_cpu_hp_callback(struct notifier_block *nb, unsigned long action, void *hcpu) { @@ -1424,6 +1424,19 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode, */ if (mode == SWITCH_FLUSH || off > 0) { if (unlikely(off == 0)) { + /* + * A final flush that encounters an empty + * sub-buffer cannot switch buffer if a + * reader is located within this sub-buffer. + * Anyway, the purpose of final flushing of a + * sub-buffer at offset 0 is to handle the case + * of entirely empty stream. + */ + if (unlikely(subbuf_trunc(offsets->begin, chan) + - subbuf_trunc((unsigned long) + atomic_long_read(&buf->consumed), chan) + >= chan->backend.buf_size)) + return -1; /* * The client does not save any header information. * Don't switch empty subbuffer on finalize, because it @@ -1503,6 +1516,48 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode m } EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow); +static void remote_switch(void *info) +{ + struct lib_ring_buffer *buf = info; + + lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE); +} + +void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf) +{ + struct channel *chan = buf->backend.chan; + const struct lib_ring_buffer_config *config = &chan->backend.config; + int ret; + + /* + * With global synchronization we don't need to use the IPI scheme. + */ + if (config->sync == RING_BUFFER_SYNC_GLOBAL) { + lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE); + return; + } + + /* + * Taking lock on CPU hotplug to ensure two things: first, that the + * target cpu is not taken concurrently offline while we are within + * smp_call_function_single() (I don't trust that get_cpu() on the + * _local_ CPU actually inhibit CPU hotplug for the _remote_ CPU (to be + * confirmed)). Secondly, if it happens that the CPU is not online, our + * own call to lib_ring_buffer_switch_slow() needs to be protected from + * CPU hotplug handlers, which can also perform a remote subbuffer + * switch. + */ + get_online_cpus(); + ret = smp_call_function_single(buf->backend.cpu, + remote_switch, buf, 1); + if (ret) { + /* Remote CPU is offline, do it ourself. */ + lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE); + } + put_online_cpus(); +} +EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote); + /* * Returns : * 0 if ok @@ -1517,9 +1572,10 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf, struct lib_ring_buffer_ctx *ctx) { const struct lib_ring_buffer_config *config = &chan->backend.config; - unsigned long reserve_commit_diff; + unsigned long reserve_commit_diff, offset_cmp; - offsets->begin = v_read(config, &buf->offset); +retry: + offsets->begin = offset_cmp = v_read(config, &buf->offset); offsets->old = offsets->begin; offsets->switch_new_start = 0; offsets->switch_new_end = 0; @@ -1551,7 +1607,7 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf, } } if (unlikely(offsets->switch_new_start)) { - unsigned long sb_index; + unsigned long sb_index, commit_count; /* * We are typically not filling the previous buffer completely. @@ -1562,12 +1618,31 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf, + config->cb.subbuffer_header_size(); /* Test new buffer integrity */ sb_index = subbuf_index(offsets->begin, chan); + /* + * Read buf->offset before buf->commit_cold[sb_index].cc_sb. + * lib_ring_buffer_check_deliver() has the matching + * memory barriers required around commit_cold cc_sb + * updates to ensure reserve and commit counter updates + * are not seen reordered when updated by another CPU. + */ + smp_rmb(); + commit_count = v_read(config, + &buf->commit_cold[sb_index].cc_sb); + /* Read buf->commit_cold[sb_index].cc_sb before buf->offset. */ + smp_rmb(); + if (unlikely(offset_cmp != v_read(config, &buf->offset))) { + /* + * The reserve counter have been concurrently updated + * while we read the commit counter. This means the + * commit counter we read might not match buf->offset + * due to concurrent update. We therefore need to retry. + */ + goto retry; + } reserve_commit_diff = (buf_trunc(offsets->begin, chan) >> chan->backend.num_subbuf_order) - - ((unsigned long) v_read(config, - &buf->commit_cold[sb_index].cc_sb) - & chan->commit_count_mask); + - (commit_count & chan->commit_count_mask); if (likely(reserve_commit_diff == 0)) { /* Next subbuffer not being written to. */ if (unlikely(config->mode != RING_BUFFER_OVERWRITE && @@ -1592,9 +1667,10 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf, } else { /* * Next subbuffer reserve offset does not match the - * commit offset. Drop record in producer-consumer and - * overwrite mode. Caused by either a writer OOPS or too - * many nested writes over a reserve/commit pair. + * commit offset, and this did not involve update to the + * reserve counter. Drop record in producer-consumer and + * overwrite mode. Caused by either a writer OOPS or + * too many nested writes over a reserve/commit pair. */ v_inc(config, &buf->records_lost_wrap); return -EIO;