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From: Corinna Vinschen <corinna@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] Cygwin: convert malloc lock to SRWLOCK Date: Wed, 27 Oct 2021 09:01:03 +0000 (GMT) [thread overview] Message-ID: <20211027090103.71A513858C27@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=44a79a6eca3d322020dda0919023d78dda129d4d commit 44a79a6eca3d322020dda0919023d78dda129d4d Author: Corinna Vinschen <corinna@vinschen.de> Date: Tue Oct 26 17:53:08 2021 +0200 Cygwin: convert malloc lock to SRWLOCK Per https://cygwin.com/pipermail/cygwin-developers/2021-October/012429.html, we may encounter a crash when starting multiple threads during process startup (here: fhandler_fifo::fixup_after_{fork,exec}) which in turn allocate memory via malloc. The problem is concurrent usage of malloc before the malloc muto has been initialized. To fix this issue, convert the muto to a SRWLOCK and make sure it is statically initalized. Thus, malloc can be called as early as necessary and malloc_init is only required to check for user space provided malloc. Note that this requires to implement a __malloc_trylock macro to be called from fork. Signed-off-by: Corinna Vinschen <corinna@vinschen.de> Diff: --- winsup/cygwin/cygmalloc.h | 8 +++++--- winsup/cygwin/dcrt0.cc | 1 + winsup/cygwin/fork.cc | 2 +- winsup/cygwin/heap.cc | 1 - winsup/cygwin/heap.h | 1 - winsup/cygwin/malloc_wrapper.cc | 4 +--- winsup/cygwin/release/3.3.0 | 4 ++++ 7 files changed, 12 insertions(+), 9 deletions(-) diff --git a/winsup/cygwin/cygmalloc.h b/winsup/cygwin/cygmalloc.h index 84bad824c..36f56294f 100644 --- a/winsup/cygwin/cygmalloc.h +++ b/winsup/cygwin/cygmalloc.h @@ -36,9 +36,11 @@ void *mmap64 (void *, size_t, int, int, int, off_t); #elif defined (__INSIDE_CYGWIN__) -# define __malloc_lock() mallock.acquire () -# define __malloc_unlock() mallock.release () -extern muto mallock; +# define __malloc_lock() AcquireSRWLockExclusive (&mallock) +# define __malloc_trylock() TryAcquireSRWLockExclusive (&mallock) +# define __malloc_unlock() ReleaseSRWLockExclusive (&mallock) +extern SRWLOCK NO_COPY mallock; +void malloc_init (); #endif diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc index 6f4723bb0..f3d09c169 100644 --- a/winsup/cygwin/dcrt0.cc +++ b/winsup/cygwin/dcrt0.cc @@ -29,6 +29,7 @@ details. */ #include "shared_info.h" #include "cygwin_version.h" #include "dll_init.h" +#include "cygmalloc.h" #include "heap.h" #include "tls_pbuf.h" #include "exception.h" diff --git a/winsup/cygwin/fork.cc b/winsup/cygwin/fork.cc index 719217856..912f17274 100644 --- a/winsup/cygwin/fork.cc +++ b/winsup/cygwin/fork.cc @@ -296,7 +296,7 @@ frok::parent (volatile char * volatile stack_here) si.lpReserved2 = (LPBYTE) &ch; si.cbReserved2 = sizeof (ch); - bool locked = __malloc_lock (); + bool locked = __malloc_trylock (); /* Remove impersonation */ cygheap->user.deimpersonate (); diff --git a/winsup/cygwin/heap.cc b/winsup/cygwin/heap.cc index b839c8cd4..f27f81bc4 100644 --- a/winsup/cygwin/heap.cc +++ b/winsup/cygwin/heap.cc @@ -230,7 +230,6 @@ user_heap_info::init () debug_printf ("heap base %p, heap top %p, heap size %ly (%lu)", base, top, chunk, chunk); page_const--; - // malloc_init (); } #define pround(n) (((size_t)(n) + page_const) & ~page_const) diff --git a/winsup/cygwin/heap.h b/winsup/cygwin/heap.h index 565758e48..25200f286 100644 --- a/winsup/cygwin/heap.h +++ b/winsup/cygwin/heap.h @@ -10,7 +10,6 @@ details. */ /* Heap management. */ void heap_init (); -void malloc_init (); #define inheap(s) \ (cygheap->user_heap.ptr && s \ diff --git a/winsup/cygwin/malloc_wrapper.cc b/winsup/cygwin/malloc_wrapper.cc index 3b245800a..2842e5398 100644 --- a/winsup/cygwin/malloc_wrapper.cc +++ b/winsup/cygwin/malloc_wrapper.cc @@ -269,13 +269,11 @@ strdup (const char *s) newlib will call __malloc_lock and __malloc_unlock at appropriate times. */ -muto NO_COPY mallock; +SRWLOCK NO_COPY mallock = SRWLOCK_INIT; void malloc_init () { - mallock.init ("mallock"); - /* Check if malloc is provided by application. If so, redirect all calls to malloc/free/realloc to application provided. This may happen if some other dll calls cygwin's malloc, but main code provides diff --git a/winsup/cygwin/release/3.3.0 b/winsup/cygwin/release/3.3.0 index 895c27397..1595b1753 100644 --- a/winsup/cygwin/release/3.3.0 +++ b/winsup/cygwin/release/3.3.0 @@ -78,3 +78,7 @@ Bug Fixes - Fix access violation that can sometimes occur when copy/pasting between 32-bit and 64-bit Cygwin environments. Align clipboard descriptor layouts. Addresses: https://cygwin.com/pipermail/cygwin-patches/2021q4/011517.html + +- Fix a synchronization issue when running multiple threads from DLL + initialization which in turn call malloc. + Addresses: https://cygwin.com/pipermail/cygwin/2021-October/249635.html
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