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musl - an implementation of the standard library for Linux-based systems
aebd6a3644
as reported by Alexey Izbyshev, there is a lock order inversion deadlock between the malloc lock and aio maplock at MT-fork time: _Fork attempts to take the aio maplock while fork already has the malloc lock, but a concurrent aio operation holding the maplock may attempt to allocate memory. move the __aio_atfork calls in the parent from _Fork to fork, and reorder the lock before most other locks, since nothing else depends on aio(*). this leaves us with the possibility that the child will not be able to obtain the read lock, if _Fork is used directly and happens concurrent with an aio operation. however, in that case, the child context is an async signal context that cannot call any further aio functions, so all we need is to ensure that close does not attempt to perform any aio cancellation. this can be achieved just by nulling out the map pointer. (*) even if other functions call close, they will only need a read lock, not a write lock, and read locks being recursive ensures they can obtain it. moreover, the number of read references held is bounded by something like twice the number of live threads, meaning that the read lock count cannot saturate. |
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| configure | ||
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musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/