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) ...@@ -263,32 +263,32 @@ static inline void raw_write_seqcount_end(seqcount_t *s)
* atomically, avoiding compiler optimizations; b) to document which writes are * atomically, avoiding compiler optimizations; b) to document which writes are
* meant to propagate to the reader critical section. This is necessary because * 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 * 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; * seqcount_t seq;
* bool X = true, Y = false; * bool X = true, Y = false;
* *
* void read(void) * void read(void)
* { * {
* bool x, y; * bool x, y;
* *
* do { * do {
* int s = read_seqcount_begin(&seq); * 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) * 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) static inline void raw_write_seqcount_barrier(seqcount_t *s)
...@@ -325,64 +325,68 @@ static inline int raw_read_seqcount_latch(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 * 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. * 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 { * struct latch_struct {
* seqcount_t seq; * seqcount_t seq;
* struct data_struct data[2]; * struct data_struct data[2];
* }; * };
* *
* Where a modification, which is assumed to be externally serialized, does the * Where a modification, which is assumed to be externally serialized, does the
* following: * following::
* *
* void latch_modify(struct latch_struct *latch, ...) * void latch_modify(struct latch_struct *latch, ...)
* { * {
* smp_wmb(); <- Ensure that the last data[1] update is visible * smp_wmb(); // Ensure that the last data[1] update is visible
* latch->seq++; * latch->seq++;
* smp_wmb(); <- Ensure that the seqcount update is visible * 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 * smp_wmb(); // Ensure that the data[0] update is visible
* latch->seq++; * latch->seq++;
* smp_wmb(); <- Ensure that the seqcount update is visible * 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 *latch_query(struct latch_struct *latch, ...)
* { * {
* struct entry *entry; * struct entry *entry;
* unsigned seq, idx; * unsigned seq, idx;
* *
* do { * do {
* seq = raw_read_seqcount_latch(&latch->seq); * seq = raw_read_seqcount_latch(&latch->seq);
* *
* idx = seq & 0x01; * idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...); * entry = data_query(latch->data[idx], ...);
* *
* smp_rmb(); * smp_rmb();
* } while (seq != latch->seq); * } while (seq != latch->seq);
* *
* return entry; * return entry;
* } * }
* *
* So during the modification, queries are first redirected to data[1]. Then we * 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] * modify data[0]. When that is complete, we redirect queries back to data[0]
* and we can modify data[1]. * and we can modify data[1].
* *
* NOTE: The non-requirement for atomic modifications does _NOT_ include * NOTE:
* the publishing of new entries in the case where data is a dynamic *
* data structure. * 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 * NOTE:
* to miss an entire modification sequence, once it resumes it might
* observe the new entry.
* *
* NOTE: When data is a dynamic data structure; one should use regular RCU * When data is a dynamic data structure; one should use regular RCU
* patterns to manage the lifetimes of the objects within. * patterns to manage the lifetimes of the objects within.
*/ */
static inline void raw_write_seqcount_latch(seqcount_t *s) static inline void raw_write_seqcount_latch(seqcount_t *s)
{ {
......
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