Commit 15cbe67b authored by Ahmed S. Darwish's avatar Ahmed S. Darwish Committed by Peter Zijlstra

seqlock: Properly format kernel-doc code samples

Align the code samples and note sections inside kernel-doc comments with
tabs. This way they can be properly parsed and rendered by Sphinx. It
also makes the code samples easier to read from text editors.
Signed-off-by: default avatarAhmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-3-a.darwish@linutronix.de
parent 0d24f65e
......@@ -263,32 +263,32 @@ static inline void raw_write_seqcount_end(seqcount_t *s)
* atomically, avoiding compiler optimizations; b) to document which writes are
* meant to propagate to the reader critical section. This is necessary because
* neither writes before and after the barrier are enclosed in a seq-writer
* critical section that would ensure readers are aware of ongoing writes.
* critical section that would ensure readers are aware of ongoing writes::
*
* seqcount_t seq;
* bool X = true, Y = false;
* seqcount_t seq;
* bool X = true, Y = false;
*
* void read(void)
* {
* bool x, y;
* void read(void)
* {
* bool x, y;
*
* do {
* int s = read_seqcount_begin(&seq);
* do {
* int s = read_seqcount_begin(&seq);
*
* x = X; y = Y;
* x = X; y = Y;
*
* } while (read_seqcount_retry(&seq, s));
* } while (read_seqcount_retry(&seq, s));
*
* BUG_ON(!x && !y);
* BUG_ON(!x && !y);
* }
*
* void write(void)
* {
* WRITE_ONCE(Y, true);
* WRITE_ONCE(Y, true);
*
* raw_write_seqcount_barrier(seq);
* raw_write_seqcount_barrier(seq);
*
* WRITE_ONCE(X, false);
* WRITE_ONCE(X, false);
* }
*/
static inline void raw_write_seqcount_barrier(seqcount_t *s)
......@@ -325,64 +325,68 @@ static inline int raw_read_seqcount_latch(seqcount_t *s)
* Very simply put: we first modify one copy and then the other. This ensures
* there is always one copy in a stable state, ready to give us an answer.
*
* The basic form is a data structure like:
* The basic form is a data structure like::
*
* struct latch_struct {
* seqcount_t seq;
* struct data_struct data[2];
* };
* struct latch_struct {
* seqcount_t seq;
* struct data_struct data[2];
* };
*
* Where a modification, which is assumed to be externally serialized, does the
* following:
* following::
*
* void latch_modify(struct latch_struct *latch, ...)
* {
* smp_wmb(); <- Ensure that the last data[1] update is visible
* latch->seq++;
* smp_wmb(); <- Ensure that the seqcount update is visible
* void latch_modify(struct latch_struct *latch, ...)
* {
* smp_wmb(); // Ensure that the last data[1] update is visible
* latch->seq++;
* smp_wmb(); // Ensure that the seqcount update is visible
*
* modify(latch->data[0], ...);
* modify(latch->data[0], ...);
*
* smp_wmb(); <- Ensure that the data[0] update is visible
* latch->seq++;
* smp_wmb(); <- Ensure that the seqcount update is visible
* smp_wmb(); // Ensure that the data[0] update is visible
* latch->seq++;
* smp_wmb(); // Ensure that the seqcount update is visible
*
* modify(latch->data[1], ...);
* }
* modify(latch->data[1], ...);
* }
*
* The query will have a form like:
* The query will have a form like::
*
* struct entry *latch_query(struct latch_struct *latch, ...)
* {
* struct entry *entry;
* unsigned seq, idx;
* struct entry *latch_query(struct latch_struct *latch, ...)
* {
* struct entry *entry;
* unsigned seq, idx;
*
* do {
* seq = raw_read_seqcount_latch(&latch->seq);
* do {
* seq = raw_read_seqcount_latch(&latch->seq);
*
* idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...);
* idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...);
*
* smp_rmb();
* } while (seq != latch->seq);
* smp_rmb();
* } while (seq != latch->seq);
*
* return entry;
* }
* return entry;
* }
*
* So during the modification, queries are first redirected to data[1]. Then we
* modify data[0]. When that is complete, we redirect queries back to data[0]
* and we can modify data[1].
*
* NOTE: The non-requirement for atomic modifications does _NOT_ include
* the publishing of new entries in the case where data is a dynamic
* data structure.
* NOTE:
*
* The non-requirement for atomic modifications does _NOT_ include
* the publishing of new entries in the case where data is a dynamic
* data structure.
*
* An iteration might start in data[0] and get suspended long enough
* to miss an entire modification sequence, once it resumes it might
* observe the new entry.
*
* An iteration might start in data[0] and get suspended long enough
* to miss an entire modification sequence, once it resumes it might
* observe the new entry.
* NOTE:
*
* NOTE: When data is a dynamic data structure; one should use regular RCU
* patterns to manage the lifetimes of the objects within.
* When data is a dynamic data structure; one should use regular RCU
* patterns to manage the lifetimes of the objects within.
*/
static inline void raw_write_seqcount_latch(seqcount_t *s)
{
......
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