The fork handler now runs so late that there is no risk anymore that
other fork handlers in the same thread use malloc, so it is no
longer necessary to install malloc hooks which made a subset
of malloc functionality available to the thread that called fork.
Previously, a thread M invoking fork would acquire locks in this order:
(M1) malloc arena locks (in the registered fork handler)
(M2) libio list lock
A thread F invoking flush (NULL) would acquire locks in this order:
(F1) libio list lock
(F2) individual _IO_FILE locks
A thread G running getdelim would use this order:
(G1) _IO_FILE lock
(G2) malloc arena lock
After executing (M1), (F1), (G1), none of the threads can make progress.
This commit changes the fork lock order to:
(M'1) libio list lock
(M'2) malloc arena locks
It explicitly encodes the lock order in the implementations of fork,
and does not rely on the registration order, thus avoiding the deadlock.
* malloc/arena.c (list_lock): Document lock ordering requirements.
(free_list_lock): New lock.
(ptmalloc_lock_all): Comment on free_list_lock.
(ptmalloc_unlock_all2): Reinitialize free_list_lock.
(detach_arena): Update comment. free_list_lock is now needed.
(_int_new_arena): Use free_list_lock around detach_arena call.
Acquire arena lock after list_lock. Add comment, including FIXME
about incorrect synchronization.
(get_free_list): Switch to free_list_lock.
(reused_arena): Acquire free_list_lock around detach_arena call
and attached threads counter update. Add two FIXMEs about
incorrect synchronization.
(arena_thread_freeres): Switch to free_list_lock.
* malloc/malloc.c (struct malloc_state): Update comments to
mention free_list_lock.
This mostly automatically-generated patch converts 113 function
definitions in glibc from old-style K&R to prototype-style. Following
my other recent such patches, this one deals with the case of function
definitions in files that either contain assertions or where grep
suggested they might contain assertions - and thus where it isn't
possible to use a simple object code comparison as a sanity check on
the correctness of the patch, because line numbers are changed.
A few such automatically-generated changes needed to be supplemented
by manual changes for the result to compile. openat64 had a prototype
declaration with "..." but an old-style definition in
sysdeps/unix/sysv/linux/dl-openat64.c, and "..." needed adding to the
generated prototype in the definition (I've filed
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68024> for diagnosing
such cases in GCC; the old state was undefined behavior not requiring
a diagnostic, but one seems a good idea). In addition, as Florian has
noted regparm attribute mismatches between declaration and definition
are only diagnosed for prototype definitions, and five functions
needed internal_function added to their definitions (in the case of
__pthread_mutex_cond_lock, via the macro definition of
__pthread_mutex_lock) to compile on i386.
After this patch is in, remaining old-style definitions are probably
most readily fixed manually before we can turn on
-Wold-style-definition for all builds.
Tested for x86_64 and x86 (testsuite).
* crypt/md5-crypt.c (__md5_crypt_r): Convert to prototype-style
function definition.
* crypt/sha256-crypt.c (__sha256_crypt_r): Likewise.
* crypt/sha512-crypt.c (__sha512_crypt_r): Likewise.
* debug/backtracesyms.c (__backtrace_symbols): Likewise.
* elf/dl-minimal.c (_itoa): Likewise.
* hurd/hurdmalloc.c (malloc): Likewise.
(free): Likewise.
(realloc): Likewise.
* inet/inet6_option.c (inet6_option_space): Likewise.
(inet6_option_init): Likewise.
(inet6_option_append): Likewise.
(inet6_option_alloc): Likewise.
(inet6_option_next): Likewise.
(inet6_option_find): Likewise.
* io/ftw.c (FTW_NAME): Likewise.
(NFTW_NAME): Likewise.
(NFTW_NEW_NAME): Likewise.
(NFTW_OLD_NAME): Likewise.
* libio/iofwide.c (_IO_fwide): Likewise.
* libio/strops.c (_IO_str_init_static_internal): Likewise.
(_IO_str_init_static): Likewise.
(_IO_str_init_readonly): Likewise.
(_IO_str_overflow): Likewise.
(_IO_str_underflow): Likewise.
(_IO_str_count): Likewise.
(_IO_str_seekoff): Likewise.
(_IO_str_pbackfail): Likewise.
(_IO_str_finish): Likewise.
* libio/wstrops.c (_IO_wstr_init_static): Likewise.
(_IO_wstr_overflow): Likewise.
(_IO_wstr_underflow): Likewise.
(_IO_wstr_count): Likewise.
(_IO_wstr_seekoff): Likewise.
(_IO_wstr_pbackfail): Likewise.
(_IO_wstr_finish): Likewise.
* locale/programs/localedef.c (normalize_codeset): Likewise.
* locale/programs/locarchive.c (add_locale_to_archive): Likewise.
(add_locales_to_archive): Likewise.
(delete_locales_from_archive): Likewise.
* malloc/malloc.c (__libc_mallinfo): Likewise.
* math/gen-auto-libm-tests.c (init_fp_formats): Likewise.
* misc/tsearch.c (__tfind): Likewise.
* nptl/pthread_attr_destroy.c (__pthread_attr_destroy): Likewise.
* nptl/pthread_attr_getdetachstate.c
(__pthread_attr_getdetachstate): Likewise.
* nptl/pthread_attr_getguardsize.c (pthread_attr_getguardsize):
Likewise.
* nptl/pthread_attr_getinheritsched.c
(__pthread_attr_getinheritsched): Likewise.
* nptl/pthread_attr_getschedparam.c
(__pthread_attr_getschedparam): Likewise.
* nptl/pthread_attr_getschedpolicy.c
(__pthread_attr_getschedpolicy): Likewise.
* nptl/pthread_attr_getscope.c (__pthread_attr_getscope):
Likewise.
* nptl/pthread_attr_getstack.c (__pthread_attr_getstack):
Likewise.
* nptl/pthread_attr_getstackaddr.c (__pthread_attr_getstackaddr):
Likewise.
* nptl/pthread_attr_getstacksize.c (__pthread_attr_getstacksize):
Likewise.
* nptl/pthread_attr_init.c (__pthread_attr_init_2_1): Likewise.
(__pthread_attr_init_2_0): Likewise.
* nptl/pthread_attr_setdetachstate.c
(__pthread_attr_setdetachstate): Likewise.
* nptl/pthread_attr_setguardsize.c (pthread_attr_setguardsize):
Likewise.
* nptl/pthread_attr_setinheritsched.c
(__pthread_attr_setinheritsched): Likewise.
* nptl/pthread_attr_setschedparam.c
(__pthread_attr_setschedparam): Likewise.
* nptl/pthread_attr_setschedpolicy.c
(__pthread_attr_setschedpolicy): Likewise.
* nptl/pthread_attr_setscope.c (__pthread_attr_setscope):
Likewise.
* nptl/pthread_attr_setstack.c (__pthread_attr_setstack):
Likewise.
* nptl/pthread_attr_setstackaddr.c (__pthread_attr_setstackaddr):
Likewise.
* nptl/pthread_attr_setstacksize.c (__pthread_attr_setstacksize):
Likewise.
* nptl/pthread_condattr_setclock.c (pthread_condattr_setclock):
Likewise.
* nptl/pthread_create.c (__find_in_stack_list): Likewise.
* nptl/pthread_getattr_np.c (pthread_getattr_np): Likewise.
* nptl/pthread_mutex_cond_lock.c (__pthread_mutex_lock): Define to
use internal_function.
* nptl/pthread_mutex_init.c (__pthread_mutex_init): Convert to
prototype-style function definition.
* nptl/pthread_mutex_lock.c (__pthread_mutex_lock): Likewise.
(__pthread_mutex_cond_lock_adjust): Likewise. Use
internal_function.
* nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock):
Convert to prototype-style function definition.
* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
Likewise.
* nptl/pthread_mutex_unlock.c (__pthread_mutex_unlock_usercnt):
Likewise.
(__pthread_mutex_unlock): Likewise.
* nptl_db/td_ta_clear_event.c (td_ta_clear_event): Likewise.
* nptl_db/td_ta_set_event.c (td_ta_set_event): Likewise.
* nptl_db/td_thr_clear_event.c (td_thr_clear_event): Likewise.
* nptl_db/td_thr_event_enable.c (td_thr_event_enable): Likewise.
* nptl_db/td_thr_set_event.c (td_thr_set_event): Likewise.
* nss/makedb.c (process_input): Likewise.
* posix/fnmatch.c (__strchrnul): Likewise.
(__wcschrnul): Likewise.
(fnmatch): Likewise.
* posix/fnmatch_loop.c (FCT): Likewise.
* posix/glob.c (globfree): Likewise.
(__glob_pattern_type): Likewise.
(__glob_pattern_p): Likewise.
* posix/regcomp.c (re_compile_pattern): Likewise.
(re_set_syntax): Likewise.
(re_compile_fastmap): Likewise.
(regcomp): Likewise.
(regerror): Likewise.
(regfree): Likewise.
* posix/regexec.c (regexec): Likewise.
(re_match): Likewise.
(re_search): Likewise.
(re_match_2): Likewise.
(re_search_2): Likewise.
(re_search_stub): Likewise. Use internal_function
(re_copy_regs): Likewise.
(re_set_registers): Convert to prototype-style function
definition.
(prune_impossible_nodes): Likewise. Use internal_function.
* resolv/inet_net_pton.c (inet_net_pton): Convert to
prototype-style function definition.
(inet_net_pton_ipv4): Likewise.
* stdlib/strtod_l.c (____STRTOF_INTERNAL): Likewise.
* sysdeps/pthread/aio_cancel.c (aio_cancel): Likewise.
* sysdeps/pthread/aio_suspend.c (aio_suspend): Likewise.
* sysdeps/pthread/timer_delete.c (timer_delete): Likewise.
* sysdeps/unix/sysv/linux/dl-openat64.c (openat64): Likewise.
Make variadic.
* time/strptime_l.c (localtime_r): Convert to prototype-style
function definition.
* wcsmbs/mbsnrtowcs.c (__mbsnrtowcs): Likewise.
* wcsmbs/mbsrtowcs_l.c (__mbsrtowcs_l): Likewise.
* wcsmbs/wcsnrtombs.c (__wcsnrtombs): Likewise.
* wcsmbs/wcsrtombs.c (__wcsrtombs): Likewise.
While doing code review I converted another bespoke round down, and
corrected a comment.
The comment spoke about keeping at least one page allocated even
during systrim, which is not correct. The code does nothing to keep
a page allocated. The code does attempt to keep PAD padding as
documented in comments and MINSIZE as required by design.
Historically in 2002 when Ulrich wrote the code (fa8d436c) the math
was inlined into one statement which did reserve an extra page:
extra = ((top_size - pad - MINSIZE + (pagesz-1)) / pagesz - 1) * pagesz;
There is no reason given for this extra page.
In 2010 Anton Branchard's change (b9b42ee0) from division
to shifts removed the extra page by dropping the "+ (pagesiz-1), which
mean we might have attempted to return -0 via MORECORE. The fix by Will
Newton in 2014 added a check for extra being zero (51a7380b).
From first principles I see no reason why we should keep an extra
page of memory from being trimmed back to the OS. The only sensible
interface is to honour PAD padding as the function is documented,
with the caveat the MINSIZE is maintained for the top chunk.
Given that we've been using this code for 5+ years with no extra
page allocated is sufficient evidence that the comment should be changed
to match the code that I'm touching.
Tested on x86_64 and i686, no regressions.
When the malloc subsystem detects some kind of memory corruption,
depending on the configuration it prints the error, a backtrace, a
memory map and then aborts the process. In this process, the
backtrace() call may result in a call to malloc, resulting in
various kinds of problematic behavior.
In one case, the malloc it calls may detect a corruption and call
backtrace again, and a stack overflow may result due to the infinite
recursion. In another case, the malloc it calls may deadlock on an
arena lock with the malloc (or free, realloc, etc.) that detected the
corruption. In yet another case, if the program is linked with
pthreads, backtrace may do a pthread_once initialization, which
deadlocks on itself.
In all these cases, the program exit is not as intended. This is
avoidable by marking the arena that malloc detected a corruption on,
as unusable. The following patch does that. Features of this patch
are as follows:
- A flag is added to the mstate struct of the arena to indicate if the
arena is corrupt.
- The flag is checked whenever malloc functions try to get a lock on
an arena. If the arena is unusable, a NULL is returned, causing the
malloc to use mmap or try the next arena.
- malloc_printerr sets the corrupt flag on the arena when it detects a
corruption
- free does not concern itself with the flag at all. It is not
important since the backtrace workflow does not need free. A free
in a parallel thread may cause another corruption, but that's not
new
- The flag check and set are not atomic and may race. This is fine
since we don't care about contention during the flag check. We want
to make sure that the malloc call in the backtrace does not trip on
itself and all that action happens in the same thread and not across
threads.
I verified that the test case does not show any regressions due to
this patch. I also ran the malloc benchmarks and found an
insignificant difference in timings (< 2%).
* malloc/Makefile (tests): New test case tst-malloc-backtrace.
* malloc/arena.c (arena_lock): Check if arena is corrupt.
(reused_arena): Find a non-corrupt arena.
(heap_trim): Pass arena to unlink.
* malloc/hooks.c (malloc_check_get_size): Pass arena to
malloc_printerr.
(top_check): Likewise.
(free_check): Likewise.
(realloc_check): Likewise.
* malloc/malloc.c (malloc_printerr): Add arena argument.
(unlink): Likewise.
(munmap_chunk): Adjust.
(ARENA_CORRUPTION_BIT): New macro.
(arena_is_corrupt): Likewise.
(set_arena_corrupt): Likewise.
(sysmalloc): Use mmap if there are no usable arenas.
(_int_malloc): Likewise.
(__libc_malloc): Don't fail if arena_get returns NULL.
(_mid_memalign): Likewise.
(__libc_calloc): Likewise.
(__libc_realloc): Adjust for additional argument to
malloc_printerr.
(_int_free): Likewise.
(malloc_consolidate): Likewise.
(_int_realloc): Likewise.
(_int_memalign): Don't touch corrupt arenas.
* malloc/tst-malloc-backtrace.c: New test case.
This seems to have been left behind as an artifact of some old changes
and can now be merged. Verified that the only generated code change
on x86_64 is that of line numbers in asserts, like so:
@@ -27253,7 +27253,7 @@ Disassembly of section .text:
416f09: 48 89 42 20 mov %rax,0x20(%rdx)
416f0d: e9 7e f6 ff ff jmpq 416590 <_int_free+0x230>
416f12: b9 3f 9f 4a 00 mov $0x4a9f3f,%ecx
- 416f17: ba d5 0f 00 00 mov $0xfd5,%edx
+ 416f17: ba d6 0f 00 00 mov $0xfd6,%edx
416f1c: be a8 9b 4a 00 mov $0x4a9ba8,%esi
416f21: bf 6a 9c 4a 00 mov $0x4a9c6a,%edi
416f26: e8 45 e8 ff ff callq 415770 <__malloc_assert>
We are replacing all of the bespoke alignment code with
ALIGN_UP, ALIGN_DOWN, PTR_ALIGN_UP, and PTR_ALIGN_DOWN.
This cleans up malloc/malloc.c, malloc/arena.c, and
elf/dl-reloc.c. It also makes all the code consistently
use pagesize, and powerof2 as required.
Code size is reduced with the removal of precomputed
pagemask, and use of pagesize instead. No measurable
difference in performance.
No regressions on x86_64.
malloc_info is defined in the same file as malloc and free, but is not
an ISO C function, so should be a weak symbol. This patch makes it
so.
Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).
[BZ #17570]
* malloc/malloc.c (malloc_info): Rename to __malloc_info and
define as weak alias of __malloc_info.
Due to my bad review suggestion for the fix for BZ #15089 a check
was removed from systrim to prevent sbrk being called with a zero
argument. Add the check back to avoid this useless work.
ChangeLog:
2014-06-19 Will Newton <will.newton@linaro.org>
* malloc/malloc.c (systrim): If extra is zero then return
early.
The current malloc_info xml output only has information about
allocations on the heap. Display information about number of mappings
and total mmapped size to this to complete the picture.
The nested function mi_arena was removed from malloc_info
and made into a non-nested static inline function of the same
name with the correct set of arguments passed from malloc_info.
This enables building glibc with compilers that don't support
nested functions. Future work on malloc_info should remove these
functions entirely to support JSON format output. Therefore we
do the minimum required to remove the nested function.
MALLOC_DEBUG is set optionally on the command line. Default the value
to zero if it is not set on the command line, and test its value
with #if rather than #ifdef. Verified the code is identical before
and after this change apart from line numbers.
ChangeLog:
2014-04-11 Will Newton <will.newton@linaro.org>
* malloc/malloc.c [!MALLOC_DEBUG]: #define MALLOC_DEBUG
to zero if it is not defined elsewhere. (mtrim): Test
the value of MALLOC_DEBUG with #if rather than #ifdef.
Objections were raised surrounding the calloc simplification
and it is better to revert the patch, continue discussions
and then submit a new patch for inclusion with all issues
fully addressed.
To make future improvements of allocator simpler we could for now calloc
just call malloc and memset. With that we could omit a changes that
would duplicate malloc changes anyway.
Perform sanity check only if we have_lock. Due to lockless nature of fastbins
we need to be careful derefencing pointers to fastbin entries (chunksize(old)
in this case) in multithreaded environments.
The fix is to add have_lock to the if-condition checks. The rest of the patch
only makes code more readable.
* malloc/malloc.c (_int_free): Perform sanity check only if we
have_lock.
A very large alignment argument passed to mealign/posix_memalign
causes _int_memalign to enter an infinite loop. Limit the maximum
alignment value to the maximum representable power of two to
prevent this from happening.
Changelog:
2013-10-30 Will Newton <will.newton@linaro.org>
[BZ #16038]
* malloc/hooks.c (memalign_check): Limit alignment to the
maximum representable power of two.
* malloc/malloc.c (__libc_memalign): Likewise.
* malloc/tst-memalign.c (do_test): Add test for very
large alignment values.
* malloc/tst-posix_memalign.c (do_test): Likewise.
for ChangeLog
* malloc/arena.c (new_heap): New memory_heap_new probe.
(grow_heap): New memory_heap_more probe.
(shrink_heap): New memory_heap_less probe.
(heap_trim): New memory_heap_free probe.
* malloc/malloc.c (sysmalloc): New memory_sbrk_more probe.
(systrim): New memory_sbrk_less probe.
* manual/probes.texi: Document them.
