christoph/lecture-operating-system-development
1
Fork 0
Code Activity

comments

Browse Source
This commit is contained in:
Christoph Urlacher
2022-07-11 19:15:30 +02:00
parent 7e9402062f
commit 60e36011e3
1 changed files with 17 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
c_os/kernel/allocator/TreeAllocator.cc
View File

@ -60,6 +60,7 @@ void* TreeAllocator::alloc(unsigned int req_size) {
unsigned int size = this->get_size(best_fit);
if constexpr (DEBUG) { kout << " - Found best-fit: " << hex << (unsigned int)best_fit << endl; }
this->rbt_remove(best_fit); // BUG: On first allocation this crashes as the tree root is being removed
if (size > HEAP_MIN_FREE_BLOCK_SIZE + rreq_size + sizeof(list_block_t)) {
// Block can be cut
if constexpr (DEBUG) { kout << " - Allocating " << dec << rreq_size << " Bytes with cutting" << endl; }
@ -75,11 +76,18 @@ void* TreeAllocator::alloc(unsigned int req_size) {
// need to remove it from the freelist, which is done for both cases
if constexpr (DEBUG) { kout << " - Allocating " << dec << rreq_size << " Bytes without cutting" << endl; }
}
// Remove the old block from the freelist
// NOTE: Originally this was placed before the leading if/else, but the red black tree code crashes
// when removing the tree root (NullPointerException bluescreen) so I moved the removal down.
// This could influence how the above rbt_insertion places the new_block, resulting in a broken
// freelist (unbalanced red black tree, not completely broken), but I didn't have time to fix this
// correctly
// BUG: If the first allocation allocates the whole heap, this removal will crash the paging
// as the freelist will no longer contain any notes, gives NullPointerException as it's not handled
// as the freelist will no longer contain any nodes, gives NullPointerException as it's not handled
// in the red black tree code (I think)
// kout << " - Removing block from freelist" << endl;
this->rbt_remove(best_fit);
// this->rbt_remove(best_fit); // HACK
if constexpr (DEBUG) { kout << " - Returned address " << hex << (unsigned int)((char*)best_fit + sizeof(list_block_t)) << endl; }
return (void*)((char*)best_fit + sizeof(list_block_t));
@ -93,7 +101,7 @@ void TreeAllocator::free(void* ptr) {
// Block already free
return;
}
block->allocated = false;
block->allocated = false; // If the block is merged backwards afterwards this is unnecessary
list_block_t* previous = block->previous;
list_block_t* next = block->next;
@ -109,11 +117,15 @@ void TreeAllocator::free(void* ptr) {
// Remove the next block from all lists as it is now part of our freed block
this->dll_remove(next);
this->rbt_remove((tree_block_t*)next);
this->rbt_remove((tree_block_t*)next); // BUG: Bluescreen if next is the only block in the freelist
if (previous->allocated) {
// Don't insert if removed later
// Don't insert if removed later because of backward merge
this->rbt_insert((tree_block_t*)block);
}
// NOTE: Originally this was placed before the leading if (after this->dll_remove(next)),
// but the red black tree code crashes when removing the tree node (like on insertion).
// Placing this here could lead to an unbalanced freelist.
// this->rbt_remove((tree_block_t*)next); // HACK
}
if (!previous->allocated) {