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commit 58d2672f64176fcb323859d3bd5240fb1cf8f25c
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Author: Wilco Dijkstra <wdijkstr@arm.com>
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Date: Fri May 10 16:38:21 2019 +0100
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Fix tcache count maximum (BZ #24531)
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The tcache counts[] array is a char, which has a very small range and thus
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may overflow. When setting tcache_count tunable, there is no overflow check.
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However the tunable must not be larger than the maximum value of the tcache
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counts[] array, otherwise it can overflow when filling the tcache.
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[BZ #24531]
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* malloc/malloc.c (MAX_TCACHE_COUNT): New define.
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(do_set_tcache_count): Only update if count is small enough.
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* manual/tunables.texi (glibc.malloc.tcache_count): Document max value.
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(cherry picked from commit 5ad533e8e65092be962e414e0417112c65d154fb)
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diff --git a/malloc/malloc.c b/malloc/malloc.c
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index 723d393f529bdb4c..92239b3324584060 100644
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--- a/malloc/malloc.c
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+++ b/malloc/malloc.c
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@@ -2919,6 +2919,8 @@ typedef struct tcache_perthread_struct
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tcache_entry *entries[TCACHE_MAX_BINS];
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} tcache_perthread_struct;
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+#define MAX_TCACHE_COUNT 127 /* Maximum value of counts[] entries. */
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+
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static __thread bool tcache_shutting_down = false;
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static __thread tcache_perthread_struct *tcache = NULL;
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@@ -5124,8 +5126,11 @@ static inline int
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__always_inline
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do_set_tcache_count (size_t value)
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{
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- LIBC_PROBE (memory_tunable_tcache_count, 2, value, mp_.tcache_count);
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- mp_.tcache_count = value;
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+ if (value <= MAX_TCACHE_COUNT)
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+ {
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+ LIBC_PROBE (memory_tunable_tcache_count, 2, value, mp_.tcache_count);
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+ mp_.tcache_count = value;
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+ }
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return 1;
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}
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diff --git a/manual/tunables.texi b/manual/tunables.texi
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index bb4819bdf1de273e..9dccf2ee7f8eec17 100644
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--- a/manual/tunables.texi
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+++ b/manual/tunables.texi
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@@ -188,8 +188,8 @@ per-thread cache. The default (and maximum) value is 1032 bytes on
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@deftp Tunable glibc.malloc.tcache_count
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The maximum number of chunks of each size to cache. The default is 7.
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-There is no upper limit, other than available system memory. If set
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-to zero, the per-thread cache is effectively disabled.
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+The upper limit is 127. If set to zero, the per-thread cache is effectively
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+disabled.
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The approximate maximum overhead of the per-thread cache is thus equal
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to the number of bins times the chunk count in each bin times the size
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