Fix newlib malloc thread safety issue #35227
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This commit adds a lock implementation for the newlib heap memory management functions (`malloc` and `free`). The `__malloc_lock` and `__malloc_unlock` functions are called by the newlib `malloc` and `free` functions to synchronise access to the heap region. Without this lock, making use of the `malloc` and `free` functions from multiple threads will result in the corruption of the heap region. Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
This commit removes the lock inside the newlib internal `_sbrk` function, which is called by `malloc` when additional heap memory is needed. This lock is no longer required because any calls to the `malloc` function are synchronised by the `__malloc_lock` and `__malloc_unlock` functions. Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
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Please ignore checkpatch warning. It's wrong. |
This commit adds a new test to verify the thread safety of the C standard functions provided by newlib. Only the memory management functions (malloc and free) are tested at this time; this test will be further extended in the future, to verify the thread safety and re-entrancy of all supported newlib functions. Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
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andyross
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May 12, 2021
| @@ -291,6 +292,18 @@ void *_sbrk(intptr_t count) | |||
| } | |||
| __weak FUNC_ALIAS(_sbrk, sbrk, void *); | |||
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| static LIBC_DATA SYS_MUTEX_DEFINE(heap_mutex); | |||
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When CONFIG_USERSPACE=n, making this a spinlock would be much smaller/faster. But they I guess someday we'll get around to implementing a futex backend for sys_mutex which would have the same property.
galak
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May 13, 2021
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This series includes a set of patches to fix the thread safety-related issue when calling the
mallocandfreefunctions from multiple threads, as well as a new test to validate the thread safety issue.Before
After
A more comprehensive series addressing the thread safety and re-entrancy issues for all newlib functions will be submitted in the future -- this series is meant to address only the most critical aspect (i.e. memory management) of the underlying problems in a timely manner.
Related to #21519 and #21518