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The recently introduced TLS variables in the thread-local destructor implementation (__cxa_thread_atexit_impl) used the default GD access model, resulting in a call to __tls_get_addr. This causes a deadlock with recent changes to the way TLS is initialized because DTV allocations are delayed and hence despite knowing the offset to the variable inside its TLS block, the thread has to take the global rtld lock to safely update the TLS offset. This causes deadlocks when a thread is instantiated and joined inside a destructor of a dlopen'd DSO. The correct long term fix is to somehow not take the lock, but that will need a lot deeper change set to alter the way in which the big rtld lock is used. Instead, this patch just eliminates the call to __tls_get_addr for the thread-local variables inside libc.so, libpthread.so and rtld by building all of their units with -mtls-model=initial-exec. There were concerns that the static storage for TLS is limited and hence we should not be using it. Additionally, dynamically loaded modules may result in libc.so looking for this static storage pretty late in static binaries. Both concerns are valid when using TLSDESC since that is where one may attempt to allocate a TLS block from static storage for even those variables that are not IE. They're not very strong arguments for the traditional TLS model though, since it assumes that the static storage would be used sparingly and definitely not by default. Hence, for now this would only theoretically affect ARM architectures. The impact is hence limited to statically linked binaries that dlopen modules that in turn load libc.so, all that on arm hardware. It seems like a small enough impact to justify fixing the larger problem that currently affects everything everywhere. This still does not solve the original problem completely. That is, it is still possible to deadlock on the big rtld lock with a small tweak to the test case attached to this patch. That problem is however not a regression in 2.22 and hence could be tackled as a separate project. The test case is picked up as is from Alex's patch. This change has been tested to verify that it does not cause any issues on x86_64. ChangeLog: [BZ #18457] * nptl/Makefile (tests): New test case tst-join7. (modules-names): New test case module tst-join7mod. * nptl/tst-join7.c: New file. * nptl/tst-join7mod.c: New file. * Makeconfig (tls-model): Pass -ftls-model=initial-exec for all translation units in libc.so, libpthread.so and rtld. |
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| benchtests | ||
| bits | ||
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| conf | ||
| conform | ||
| crypt | ||
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| debug | ||
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| malloc | ||
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| math | ||
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| stdio-common | ||
| stdlib | ||
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| configure | ||
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| Makeconfig | ||
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| README | ||
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| version.h | ||
| WUR-REPORT | ||
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 2.6.32 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at http://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see http://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.