path: root/src/mman/munmap.c
AgeCommit message (Collapse)AuthorLines
2018-09-12reduce spurious inclusion of libc.hRich Felker-1/+0
libc.h was intended to be a header for access to global libc state and related interfaces, but ended up included all over the place because it was the way to get the weak_alias macro. most of the inclusions removed here are places where weak_alias was needed. a few were recently introduced for hidden. some go all the way back to when libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented) cancellation points had to include it. remaining spurious users are mostly callers of the LOCK/UNLOCK macros and files that use the LFS64 macro to define the awful *64 aliases. in a few places, new inclusion of libc.h is added because several internal headers no longer implicitly include libc.h. declarations for __lockfile and __unlockfile are moved from libc.h to stdio_impl.h so that the latter does not need libc.h. putting them in libc.h made no sense at all, since the macros in stdio_impl.h are needed to use them correctly anyway.
2015-04-10redesign and simplify vmlock systemRich Felker-9/+4
this global lock allows certain unlock-type primitives to exclude mmap/munmap operations which could change the identity of virtual addresses while references to them still exist. the original design mistakenly assumed mmap/munmap would conversely need to exclude the same operations which exclude mmap/munmap, so the vmlock was implemented as a sort of 'symmetric recursive rwlock'. this turned out to be unnecessary. commit 25d12fc0fc51f1fae0f85b4649a6463eb805aa8f already shortened the interval during which mmap/munmap held their side of the lock, but left the inappropriate lock design and some inefficiency. the new design uses a separate function, __vm_wait, which does not hold any lock itself and only waits for lock users which were already present when it was called to release the lock. this is sufficient because of the way operations that need to be excluded are sequenced: the "unlock-type" operations using the vmlock need only block mmap/munmap operations that are precipitated by (and thus sequenced after) the atomic-unlock they perform while holding the vmlock. this allows for a spectacular lack of synchronization in the __vm_wait function itself.
2014-08-16optimize locking against vm changes for mmap/munmapRich Felker-1/+1
the whole point of this locking is to prevent munmap, or mmap with MAP_FIXED, from deallocating virtual addresses, or changing the backing a given virtual address refers to, during certain race windows involving self-synchronized unmapping or destruction of pthread synchronization objects. there is no need for exclusion in the other direction, so it suffices to take the lock momentarily and release it before making the syscall, rather than holding it across the syscall.
2013-12-12include cleanups: remove unused headers and add feature test macrosSzabolcs Nagy-1/+0
2011-09-27process-shared barrier support, based on discussion with bdonlanRich Felker-1/+10
this implementation is rather heavy-weight, but it's the first solution i've found that's actually correct. all waiters actually wait twice at the barrier so that they can synchronize exit, and they hold a "vm lock" that prevents changes to virtual memory mappings (and blocks pthread_barrier_destroy) until all waiters are finished inspecting the barrier. thus, it is safe for any thread to destroy and/or unmap the barrier's memory as soon as pthread_barrier_wait returns, without further synchronization.
2011-03-20global cleanup to use the new syscall interfaceRich Felker-1/+1
2011-02-12initial check-in, version 0.5.0v0.5.0Rich Felker-0/+11