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| @@ -263,32 +263,32 @@ static inline void raw_write_seqcount_end(seqcount_t *s) · 262 unmodified lines | ||
| 263 | 263 | * atomically, avoiding compiler optimizations; b) to document which writes are |
| 264 | 264 | * meant to propagate to the reader critical section. This is necessary because |
| 265 | 265 | * neither writes before and after the barrier are enclosed in a seq-writer |
| 266 | − * critical section that would ensure readers are aware of ongoing writes. | |
| 266 | + * critical section that would ensure readers are aware of ongoing writes:: | |
| 267 | 267 | * |
| 268 | − * seqcount_t seq; | |
| 269 | − * bool X = true, Y = false; | |
| 268 | + * seqcount_t seq; | |
| 269 | + * bool X = true, Y = false; | |
| 270 | 270 | * |
| 271 | − * void read(void) | |
| 272 | − * { | |
| 273 | − * bool x, y; | |
| 271 | + * void read(void) | |
| 272 | + * { | |
| 273 | + * bool x, y; | |
| 274 | 274 | * |
| 275 | − * do { | |
| 276 | − * int s = read_seqcount_begin(&seq); | |
| 275 | + * do { | |
| 276 | + * int s = read_seqcount_begin(&seq); | |
| 277 | 277 | * |
| 278 | − * x = X; y = Y; | |
| 278 | + * x = X; y = Y; | |
| 279 | 279 | * |
| 280 | − * } while (read_seqcount_retry(&seq, s)); | |
| 280 | + * } while (read_seqcount_retry(&seq, s)); | |
| 281 | 281 | * |
| 282 | − * BUG_ON(!x && !y); | |
| 282 | + * BUG_ON(!x && !y); | |
| 283 | 283 | * } |
| 284 | 284 | * |
| 285 | 285 | * void write(void) |
| 286 | 286 | * { |
| 287 | − * WRITE_ONCE(Y, true); | |
| 287 | + * WRITE_ONCE(Y, true); | |
| 288 | 288 | * |
| 289 | − * raw_write_seqcount_barrier(seq); | |
| 289 | + * raw_write_seqcount_barrier(seq); | |
| 290 | 290 | * |
| 291 | − * WRITE_ONCE(X, false); | |
| 291 | + * WRITE_ONCE(X, false); | |
| 292 | 292 | * } |
| 293 | 293 | */ |
| 294 | 294 | static inline void raw_write_seqcount_barrier(seqcount_t *s) |
| @@ -325,64 +325,68 @@ static inline int raw_read_seqcount_latch(seqcount_t *s) · 30 unmodified lines | ||
| 325 | 325 | * Very simply put: we first modify one copy and then the other. This ensures |
| 326 | 326 | * there is always one copy in a stable state, ready to give us an answer. |
| 327 | 327 | * |
| 328 | − * The basic form is a data structure like: | |
| 328 | + * The basic form is a data structure like:: | |
| 329 | 329 | * |
| 330 | − * struct latch_struct { | |
| 331 | − * seqcount_t seq; | |
| 332 | − * struct data_struct data[2]; | |
| 333 | − * }; | |
| 330 | + * struct latch_struct { | |
| 331 | + * seqcount_t seq; | |
| 332 | + * struct data_struct data[2]; | |
| 333 | + * }; | |
| 334 | 334 | * |
| 335 | 335 | * Where a modification, which is assumed to be externally serialized, does the |
| 336 | − * following: | |
| 336 | + * following:: | |
| 337 | 337 | * |
| 338 | − * void latch_modify(struct latch_struct *latch, ...) | |
| 339 | − * { | |
| 340 | − * smp_wmb(); <- Ensure that the last data[1] update is visible | |
| 341 | − * latch->seq++; | |
| 342 | − * smp_wmb(); <- Ensure that the seqcount update is visible | |
| 338 | + * void latch_modify(struct latch_struct *latch, ...) | |
| 339 | + * { | |
| 340 | + * smp_wmb(); // Ensure that the last data[1] update is visible | |
| 341 | + * latch->seq++; | |
| 342 | + * smp_wmb(); // Ensure that the seqcount update is visible | |
| 343 | 343 | * |
| 344 | − * modify(latch->data[0], ...); | |
| 344 | + * modify(latch->data[0], ...); | |
| 345 | 345 | * |
| 346 | − * smp_wmb(); <- Ensure that the data[0] update is visible | |
| 347 | − * latch->seq++; | |
| 348 | − * smp_wmb(); <- Ensure that the seqcount update is visible | |
| 346 | + * smp_wmb(); // Ensure that the data[0] update is visible | |
| 347 | + * latch->seq++; | |
| 348 | + * smp_wmb(); // Ensure that the seqcount update is visible | |
| 349 | 349 | * |
| 350 | − * modify(latch->data[1], ...); | |
| 351 | − * } | |
| 350 | + * modify(latch->data[1], ...); | |
| 351 | + * } | |
| 352 | 352 | * |
| 353 | − * The query will have a form like: | |
| 353 | + * The query will have a form like:: | |
| 354 | 354 | * |
| 355 | − * struct entry *latch_query(struct latch_struct *latch, ...) | |
| 356 | − * { | |
| 357 | − * struct entry *entry; | |
| 358 | − * unsigned seq, idx; | |
| 355 | + * struct entry *latch_query(struct latch_struct *latch, ...) | |
| 356 | + * { | |
| 357 | + * struct entry *entry; | |
| 358 | + * unsigned seq, idx; | |
| 359 | 359 | * |
| 360 | − * do { | |
| 361 | − * seq = raw_read_seqcount_latch(&latch->seq); | |
| 360 | + * do { | |
| 361 | + * seq = raw_read_seqcount_latch(&latch->seq); | |
| 362 | 362 | * |
| 363 | − * idx = seq & 0x01; | |
| 364 | − * entry = data_query(latch->data[idx], ...); | |
| 363 | + * idx = seq & 0x01; | |
| 364 | + * entry = data_query(latch->data[idx], ...); | |
| 365 | 365 | * |
| 366 | − * smp_rmb(); | |
| 367 | − * } while (seq != latch->seq); | |
| 366 | + * smp_rmb(); | |
| 367 | + * } while (seq != latch->seq); | |
| 368 | 368 | * |
| 369 | − * return entry; | |
| 370 | − * } | |
| 369 | + * return entry; | |
| 370 | + * } | |
| 371 | 371 | * |
| 372 | 372 | * So during the modification, queries are first redirected to data[1]. Then we |
| 373 | 373 | * modify data[0]. When that is complete, we redirect queries back to data[0] |
| 374 | 374 | * and we can modify data[1]. |
| 375 | 375 | * |
| 376 | − * NOTE: The non-requirement for atomic modifications does _NOT_ include | |
| 377 | − * the publishing of new entries in the case where data is a dynamic | |
| 378 | − * data structure. | |
| 376 | + * NOTE: | |
| 377 | + * | |
| 378 | + * The non-requirement for atomic modifications does _NOT_ include | |
| 379 | + * the publishing of new entries in the case where data is a dynamic | |
| 380 | + * data structure. | |
| 381 | + * | |
| 382 | + * An iteration might start in data[0] and get suspended long enough | |
| 383 | + * to miss an entire modification sequence, once it resumes it might | |
| 384 | + * observe the new entry. | |
| 379 | 385 | * |
| 380 | − * An iteration might start in data[0] and get suspended long enough | |
| 381 | − * to miss an entire modification sequence, once it resumes it might | |
| 382 | − * observe the new entry. | |
| 386 | + * NOTE: | |
| 383 | 387 | * |
| 384 | − * NOTE: When data is a dynamic data structure; one should use regular RCU | |
| 385 | − * patterns to manage the lifetimes of the objects within. | |
| 388 | + * When data is a dynamic data structure; one should use regular RCU | |
| 389 | + * patterns to manage the lifetimes of the objects within. | |
| 386 | 390 | */ |
| 387 | 391 | static inline void raw_write_seqcount_latch(seqcount_t *s) |
| 388 | 392 | { |