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[release/6.0] Fix bug where we reference the entry #0 in the pinned plug queue #63351

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Merged
jeffschwMSFT merged 1 commit into from
Jan 6, 2022
Merged

[release/6.0] Fix bug where we reference the entry #0 in the pinned plug queue #63351

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Fix bug where we reference the entry #0 in the pinned plug queue (#60966 
)

We reference entry #0 in the pinned plug queue even if there are no pinned plugs at all and thus the pinned plug queue contains left-over data from the mark phase.

The fix is to initialize saved_pinned_plug_index to a value that is invalid as a pinned plug queue index, and only use saved_pinned_plug_index as an index if  is valid.
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@PeterSolMS @cshung
PeterSolMS authored and cshung committed Jan 4, 2022
commit 23b2c4d1e3f5aa37f67952a25e217b0e807d7698
19 changes: 16 additions & 3 deletions src/coreclr/gc/gc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2725,7 +2725,7 @@ alloc_list gc_heap::poh_alloc_list [NUM_POH_ALIST-1];
#ifdef DOUBLY_LINKED_FL
// size we removed with no undo; only for recording purpose
size_t gc_heap::gen2_removed_no_undo = 0;
size_t gc_heap::saved_pinned_plug_index = 0;
size_t gc_heap::saved_pinned_plug_index = INVALID_SAVED_PINNED_PLUG_INDEX;
#endif //DOUBLY_LINKED_FL

#ifdef FEATURE_EVENT_TRACE
Expand Down Expand Up @@ -13903,7 +13903,20 @@ void gc_heap::adjust_limit (uint8_t* start, size_t limit_size, generation* gen)
uint8_t* old_loc = generation_last_free_list_allocated (gen);

// check if old_loc happens to be in a saved plug_and_gap with a pinned plug after it
uint8_t* saved_plug_and_gap = pinned_plug (pinned_plug_of (saved_pinned_plug_index)) - sizeof(plug_and_gap);
uint8_t* saved_plug_and_gap = nullptr;
if (saved_pinned_plug_index != INVALID_SAVED_PINNED_PLUG_INDEX)
{
saved_plug_and_gap = pinned_plug (pinned_plug_of (saved_pinned_plug_index)) - sizeof(plug_and_gap);

dprintf (3333, ("[h%d] sppi: %Id mtos: %Id old_loc: %Ix pp: %Ix(%Id) offs: %Id",
heap_number,
saved_pinned_plug_index,
mark_stack_tos,
old_loc,
pinned_plug (pinned_plug_of (saved_pinned_plug_index)),
pinned_len (pinned_plug_of (saved_pinned_plug_index)),
old_loc - saved_plug_and_gap));
}
size_t offset = old_loc - saved_plug_and_gap;
if (offset < sizeof(gap_reloc_pair))
{
Expand Down Expand Up @@ -27519,7 +27532,7 @@ void gc_heap::plan_phase (int condemned_gen_number)

#ifdef DOUBLY_LINKED_FL
gen2_removed_no_undo = 0;
saved_pinned_plug_index = 0;
saved_pinned_plug_index = INVALID_SAVED_PINNED_PLUG_INDEX;
#endif //DOUBLY_LINKED_FL

while (1)
Expand Down
2 changes: 2 additions & 0 deletions src/coreclr/gc/gcpriv.h
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Expand Up @@ -4496,6 +4496,8 @@ class gc_heap
PER_HEAP
size_t gen2_removed_no_undo;

#define INVALID_SAVED_PINNED_PLUG_INDEX ((size_t)~0)

PER_HEAP
size_t saved_pinned_plug_index;
#endif //DOUBLY_LINKED_FL
Expand Down