X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=lib%2Fringbuffer%2Fring_buffer_frontend.c;h=5043105e465ffcac0633d930f8f91cb03b2272da;hb=510f66d17bb0cddb209ac01db1ed5be3da49a567;hp=92aa78f57ddf2ed95f42c16e23728d32f58291b6;hpb=294d35794ac83c4321e4bd3d56317844771517ae;p=lttng-modules.git diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c index 92aa78f5..5043105e 100644 --- a/lib/ringbuffer/ring_buffer_frontend.c +++ b/lib/ringbuffer/ring_buffer_frontend.c @@ -1015,7 +1015,7 @@ retry: */ if (((commit_count - chan->backend.subbuf_size) & chan->commit_count_mask) - - (buf_trunc(consumed_cur, chan) + - (buf_trunc(consumed, chan) >> chan->backend.num_subbuf_order) != 0) goto nodata; @@ -1024,7 +1024,7 @@ retry: * Check that we are not about to read the same subbuffer in * which the writer head is. */ - if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_cur, chan) + if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed, chan) == 0) goto nodata; @@ -1249,7 +1249,7 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf, commit_count = v_read(config, &buf->commit_hot[oldidx].cc); /* Check if the written buffer has to be delivered */ lib_ring_buffer_check_deliver(config, buf, chan, offsets->old, - commit_count, oldidx); + commit_count, oldidx, tsc); lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx, offsets->old, commit_count, config->cb.subbuffer_header_size()); @@ -1293,7 +1293,7 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf, v_add(config, padding_size, &buf->commit_hot[oldidx].cc); commit_count = v_read(config, &buf->commit_hot[oldidx].cc); lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1, - commit_count, oldidx); + commit_count, oldidx, tsc); lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx, offsets->old, commit_count, padding_size); @@ -1336,7 +1336,7 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf, commit_count = v_read(config, &buf->commit_hot[beginidx].cc); /* Check if the written buffer has to be delivered */ lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin, - commit_count, beginidx); + commit_count, beginidx, tsc); lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx, offsets->begin, commit_count, config->cb.subbuffer_header_size()); @@ -1397,7 +1397,7 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode, u64 *tsc) { const struct lib_ring_buffer_config *config = &chan->backend.config; - unsigned long off; + unsigned long off, reserve_commit_diff; offsets->begin = v_read(config, &buf->offset); offsets->old = offsets->begin; @@ -1422,36 +1422,68 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode, * (records and header timestamps) are visible to the reader. This is * required for quiescence guarantees for the fusion merge. */ - 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 - * is invalid to deliver a completely empty subbuffer. - */ - if (!config->cb.subbuffer_header_size()) + if (mode != SWITCH_FLUSH && !off) + return -1; /* we do not have to switch : buffer is empty */ + + if (unlikely(off == 0)) { + unsigned long sb_index, commit_count; + + /* + * We are performing a SWITCH_FLUSH. At this stage, there are no + * concurrent writes into the buffer. + * + * The client does not save any header information. Don't + * switch empty subbuffer on finalize, because it is invalid to + * deliver a completely empty subbuffer. + */ + if (!config->cb.subbuffer_header_size()) + return -1; + + /* Test new buffer integrity */ + sb_index = subbuf_index(offsets->begin, chan); + commit_count = v_read(config, + &buf->commit_cold[sb_index].cc_sb); + reserve_commit_diff = + (buf_trunc(offsets->begin, chan) + >> chan->backend.num_subbuf_order) + - (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 && + subbuf_trunc(offsets->begin, chan) + - subbuf_trunc((unsigned long) + atomic_long_read(&buf->consumed), chan) + >= chan->backend.buf_size)) { + /* + * We do not overwrite non consumed buffers + * and we are full : don't switch. + */ return -1; + } else { + /* + * Next subbuffer not being written to, and we + * are either in overwrite mode or the buffer is + * not full. It's safe to write in this new + * subbuffer. + */ + } + } else { /* - * Need to write the subbuffer start header on finalize. + * Next subbuffer reserve offset does not match the + * commit offset. Don't perform switch in + * producer-consumer and overwrite mode. Caused by + * either a writer OOPS or too many nested writes over a + * reserve/commit pair. */ - offsets->switch_old_start = 1; + return -1; } - offsets->begin = subbuf_align(offsets->begin, chan); - } else - return -1; /* we do not have to switch : buffer is empty */ + + /* + * Need to write the subbuffer start header on finalize. + */ + offsets->switch_old_start = 1; + } + offsets->begin = subbuf_align(offsets->begin, chan); /* Note: old points to the next subbuf at offset 0 */ offsets->end = offsets->begin; return 0; @@ -1572,9 +1604,10 @@ 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; @@ -1606,7 +1639,7 @@ 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. @@ -1617,12 +1650,31 @@ 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 && @@ -1647,9 +1699,10 @@ 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;