diff options
| -rw-r--r-- | fs/aio.c | 120 |
1 files changed, 67 insertions, 53 deletions
@@ -52,7 +52,8 @@ struct aio_ring { unsigned id; /* kernel internal index number */ unsigned nr; /* number of io_events */ - unsigned head; + unsigned head; /* Written to by userland or under ring_lock + * mutex by aio_read_events_ring(). */ unsigned tail; unsigned magic; @@ -243,6 +244,11 @@ static void aio_free_ring(struct kioctx *ctx) { int i; + /* Disconnect the kiotx from the ring file. This prevents future + * accesses to the kioctx from page migration. + */ + put_aio_ring_file(ctx); + for (i = 0; i < ctx->nr_pages; i++) { struct page *page; pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i, @@ -254,8 +260,6 @@ static void aio_free_ring(struct kioctx *ctx) put_page(page); } - put_aio_ring_file(ctx); - if (ctx->ring_pages && ctx->ring_pages != ctx->internal_pages) { kfree(ctx->ring_pages); ctx->ring_pages = NULL; @@ -283,29 +287,38 @@ static int aio_migratepage(struct address_space *mapping, struct page *new, { struct kioctx *ctx; unsigned long flags; + pgoff_t idx; int rc; rc = 0; - /* Make sure the old page hasn't already been changed */ + /* mapping->private_lock here protects against the kioctx teardown. */ spin_lock(&mapping->private_lock); ctx = mapping->private_data; - if (ctx) { - pgoff_t idx; - spin_lock_irqsave(&ctx->completion_lock, flags); - idx = old->index; - if (idx < (pgoff_t)ctx->nr_pages) { - if (ctx->ring_pages[idx] != old) - rc = -EAGAIN; - } else - rc = -EINVAL; - spin_unlock_irqrestore(&ctx->completion_lock, flags); + if (!ctx) { + rc = -EINVAL; + goto out; + } + + /* The ring_lock mutex. The prevents aio_read_events() from writing + * to the ring's head, and prevents page migration from mucking in + * a partially initialized kiotx. + */ + if (!mutex_trylock(&ctx->ring_lock)) { + rc = -EAGAIN; + goto out; + } + + idx = old->index; + if (idx < (pgoff_t)ctx->nr_pages) { + /* Make sure the old page hasn't already been changed */ + if (ctx->ring_pages[idx] != old) + rc = -EAGAIN; } else rc = -EINVAL; - spin_unlock(&mapping->private_lock); if (rc != 0) - return rc; + goto out_unlock; /* Writeback must be complete */ BUG_ON(PageWriteback(old)); @@ -314,38 +327,26 @@ static int aio_migratepage(struct address_space *mapping, struct page *new, rc = migrate_page_move_mapping(mapping, new, old, NULL, mode, 1); if (rc != MIGRATEPAGE_SUCCESS) { put_page(new); - return rc; + goto out_unlock; } - /* We can potentially race against kioctx teardown here. Use the - * address_space's private data lock to protect the mapping's - * private_data. + /* Take completion_lock to prevent other writes to the ring buffer + * while the old page is copied to the new. This prevents new + * events from being lost. */ - spin_lock(&mapping->private_lock); - ctx = mapping->private_data; - if (ctx) { - pgoff_t idx; - spin_lock_irqsave(&ctx->completion_lock, flags); - migrate_page_copy(new, old); - idx = old->index; - if (idx < (pgoff_t)ctx->nr_pages) { - /* And only do the move if things haven't changed */ - if (ctx->ring_pages[idx] == old) - ctx->ring_pages[idx] = new; - else - rc = -EAGAIN; - } else - rc = -EINVAL; - spin_unlock_irqrestore(&ctx->completion_lock, flags); - } else - rc = -EBUSY; - spin_unlock(&mapping->private_lock); + spin_lock_irqsave(&ctx->completion_lock, flags); + migrate_page_copy(new, old); + BUG_ON(ctx->ring_pages[idx] != old); + ctx->ring_pages[idx] = new; + spin_unlock_irqrestore(&ctx->completion_lock, flags); - if (rc == MIGRATEPAGE_SUCCESS) - put_page(old); - else - put_page(new); + /* The old page is no longer accessible. */ + put_page(old); +out_unlock: + mutex_unlock(&ctx->ring_lock); +out: + spin_unlock(&mapping->private_lock); return rc; } #endif @@ -380,7 +381,7 @@ static int aio_setup_ring(struct kioctx *ctx) file = aio_private_file(ctx, nr_pages); if (IS_ERR(file)) { ctx->aio_ring_file = NULL; - return -EAGAIN; + return -ENOMEM; } ctx->aio_ring_file = file; @@ -415,7 +416,7 @@ static int aio_setup_ring(struct kioctx *ctx) if (unlikely(i != nr_pages)) { aio_free_ring(ctx); - return -EAGAIN; + return -ENOMEM; } ctx->mmap_size = nr_pages * PAGE_SIZE; @@ -429,7 +430,7 @@ static int aio_setup_ring(struct kioctx *ctx) if (IS_ERR((void *)ctx->mmap_base)) { ctx->mmap_size = 0; aio_free_ring(ctx); - return -EAGAIN; + return -ENOMEM; } pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base); @@ -556,6 +557,10 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm) rcu_read_unlock(); spin_unlock(&mm->ioctx_lock); + /* While kioctx setup is in progress, + * we are protected from page migration + * changes ring_pages by ->ring_lock. + */ ring = kmap_atomic(ctx->ring_pages[0]); ring->id = ctx->id; kunmap_atomic(ring); @@ -640,24 +645,28 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) ctx->max_reqs = nr_events; - if (percpu_ref_init(&ctx->users, free_ioctx_users)) - goto err; - - if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs)) - goto err; - spin_lock_init(&ctx->ctx_lock); spin_lock_init(&ctx->completion_lock); mutex_init(&ctx->ring_lock); + /* Protect against page migration throughout kiotx setup by keeping + * the ring_lock mutex held until setup is complete. */ + mutex_lock(&ctx->ring_lock); init_waitqueue_head(&ctx->wait); INIT_LIST_HEAD(&ctx->active_reqs); + if (percpu_ref_init(&ctx->users, free_ioctx_users)) + goto err; + + if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs)) + goto err; + ctx->cpu = alloc_percpu(struct kioctx_cpu); if (!ctx->cpu) goto err; - if (aio_setup_ring(ctx) < 0) + err = aio_setup_ring(ctx); + if (err < 0) goto err; atomic_set(&ctx->reqs_available, ctx->nr_events - 1); @@ -683,6 +692,9 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) if (err) goto err_cleanup; + /* Release the ring_lock mutex now that all setup is complete. */ + mutex_unlock(&ctx->ring_lock); + pr_debug("allocated ioctx %p[%ld]: mm=%p mask=0x%x\n", ctx, ctx->user_id, mm, ctx->nr_events); return ctx; @@ -692,6 +704,7 @@ err_cleanup: err_ctx: aio_free_ring(ctx); err: + mutex_unlock(&ctx->ring_lock); free_percpu(ctx->cpu); free_percpu(ctx->reqs.pcpu_count); free_percpu(ctx->users.pcpu_count); @@ -1024,6 +1037,7 @@ static long aio_read_events_ring(struct kioctx *ctx, mutex_lock(&ctx->ring_lock); + /* Access to ->ring_pages here is protected by ctx->ring_lock. */ ring = kmap_atomic(ctx->ring_pages[0]); head = ring->head; tail = ring->tail; |
