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AK: Fix Bitmap not finding unset ranges at the end of the map

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When we switched the Bitmap code to operating 32 bits at a time,
we neglected to look in the trailing remainder bits after the last
full 32-bit word.

This patch fixes that and adds a couple of tests for Bitmap that I
hacked up while tracking down this bug.

I found this bug when noticing that the kernel would OOM while there
were still some pages left in the physical page allocator.
This commit is contained in:
Andreas Kling 2020-05-06 20:14:59 +02:00
parent 8182a709e3
commit bf7b77e252
2 changed files with 152 additions and 1 deletions
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14
AK/Bitmap.h
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@ -243,6 +243,18 @@ public:
}
if (free_chunks < min_length) {
size_t first_trailing_bit = (m_size / 32) * 32;
size_t trailing_bits = size() % 32;
for (size_t i = 0; i < trailing_bits; ++i) {
if (!get(first_trailing_bit + i)) {
if (!free_chunks)
*start_of_free_chunks = first_trailing_bit + i;
if (++free_chunks >= min_length)
return min(free_chunks, max_length);
} else {
free_chunks = 0;
}
}
return {};
}
@ -340,7 +352,7 @@ public:
static constexpr u32 max_size = 0xffffffff;
private:
size_t size_in_bytes() const { return ceil_div(m_size, 8); }
size_t size_in_bytes() const { return ceil_div(m_size, static_cast<size_t>(8)); }
u8* m_data { nullptr };
size_t m_size { 0 };