The kmsg_dumper can be called from any context and CPU, possibly from multiple CPUs simultaneously. Since the writing of the buffer can occur from a later scheduled work queue, the oops buffer must be protected against simultaneous dumping. Use an atomic bit to mark when the buffer is protected. Release the protection in between setting the buffer and the actual writing in order for a possible panic (immediate write) to be written during the scheduling of a previous oops (delayed write). An atomic bit (rather than a spinlock) was chosen so that no scheduling or preemption side-effects would be introduced. The MTD kmsg_dumper may dump directly or it may be delayed (via scheduled work). Depending on the context, different MTD callbacks are used. For example, mtd_write() expects to be called in a non-atomic context and may take a mutex.
Unified · Split
| @@ -52,6 +52,7 @@ static struct mtdoops_context { · 51 unmodified lines | ||
| 52 | 52 | int nextcount; |
| 53 | 53 | unsigned long *oops_page_used; |
| 54 | 54 | |
| 55 | + unsigned long oops_buf_busy; | |
| 55 | 56 | void *oops_buf; |
| 56 | 57 | } oops_cxt; |
| 57 | 58 | |
| @@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) · 122 unmodified lines | ||
| 180 | 181 | u32 *hdr; |
| 181 | 182 | int ret; |
| 182 | 183 | |
| 184 | + if (test_and_set_bit(0, &cxt->oops_buf_busy)) | |
| 185 | + return; | |
| 186 | + | |
| 183 | 187 | /* Add mtdoops header to the buffer */ |
| 184 | 188 | hdr = cxt->oops_buf; |
| 185 | 189 | hdr[0] = cxt->nextcount; |
| @@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) · 4 unmodified lines | ||
| 190 | 194 | record_size, &retlen, cxt->oops_buf); |
| 191 | 195 | if (ret == -EOPNOTSUPP) { |
| 192 | 196 | printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n"); |
| 193 | − return; | |
| 197 | + goto out; | |
| 194 | 198 | } |
| 195 | 199 | } else |
| 196 | 200 | ret = mtd_write(mtd, cxt->nextpage * record_size, |
| @@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) · 6 unmodified lines | ||
| 203 | 207 | memset(cxt->oops_buf, 0xff, record_size); |
| 204 | 208 | |
| 205 | 209 | mtdoops_inc_counter(cxt); |
| 210 | +out: | |
| 211 | + clear_bit(0, &cxt->oops_buf_busy); | |
| 206 | 212 | } |
| 207 | 213 | |
| 208 | 214 | static void mtdoops_workfunc_write(struct work_struct *work) |
| @@ -276,8 +282,11 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper, · 67 unmodified lines | ||
| 276 | 282 | if (reason == KMSG_DUMP_OOPS && !dump_oops) |
| 277 | 283 | return; |
| 278 | 284 | |
| 285 | + if (test_and_set_bit(0, &cxt->oops_buf_busy)) | |
| 286 | + return; | |
| 279 | 287 | kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE, |
| 280 | 288 | record_size - MTDOOPS_HEADER_SIZE, NULL); |
| 289 | + clear_bit(0, &cxt->oops_buf_busy); | |
| 281 | 290 | |
| 282 | 291 | if (reason != KMSG_DUMP_OOPS) { |
| 283 | 292 | /* Panics must be written immediately */ |
| @@ -394,6 +403,7 @@ static int __init mtdoops_init(void) · 110 unmodified lines | ||
| 394 | 403 | return -ENOMEM; |
| 395 | 404 | } |
| 396 | 405 | memset(cxt->oops_buf, 0xff, record_size); |
| 406 | + cxt->oops_buf_busy = 0; | |
| 397 | 407 | |
| 398 | 408 | INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase); |
| 399 | 409 | INIT_WORK(&cxt->work_write, mtdoops_workfunc_write); |