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Commit4621c7f

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Avoid SIGBUS on Linux when a DSM memory request overruns tmpfs.
On Linux, shared memory segments created with shm_open() are backed byswap files created in tmpfs. If the swap file needs to be extended,but there's no tmpfs space left, you get a very unfriendly SIGBUS trap.To avoid this, force allocation of the full request size when we createthe segment. This adds a few cycles, but none that we wouldn't expendlater anyway, assuming the request isn't hugely bigger than the actualneed.Make this code #ifdef __linux__, because (a) there's not currently areason to think the same problem exists on other platforms, and (b)applying posix_fallocate() to an FD created by shm_open() isn't veryportable anyway.Back-patch to 9.4 where the DSM code came in.Thomas Munro, per a bug report from Amul SulDiscussion:https://postgr.es/m/1002664500.12301802.1471008223422.JavaMail.yahoo@mail.yahoo.com
1 parent99e90ba commit4621c7f

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5 files changed

+60
-4
lines changed

5 files changed

+60
-4
lines changed

‎configure‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -13024,7 +13024,7 @@ fi
1302413024
LIBS_including_readline="$LIBS"
1302513025
LIBS=`echo"$LIBS"| sed -e's/-ledit//g' -e's/-lreadline//g'`
1302613026

13027-
forac_funcin cbrt clock_gettime dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
13027+
forac_funcin cbrt clock_gettime dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove pollposix_fallocatepstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
1302813028
do:
1302913029
as_ac_var=`$as_echo"ac_cv_func_$ac_func"|$as_tr_sh`
1303013030
ac_fn_c_check_func"$LINENO""$ac_func""$as_ac_var"

‎configure.in‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1430,7 +1430,7 @@ PGAC_FUNC_WCSTOMBS_L
14301430
LIBS_including_readline="$LIBS"
14311431
LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
14321432

1433-
AC_CHECK_FUNCS([cbrt clock_gettime dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
1433+
AC_CHECK_FUNCS([cbrt clock_gettime dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove pollposix_fallocatepstat pthread_is_threaded_np readlink setproctitle setsid shm_open symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
14341434

14351435
AC_REPLACE_FUNCS(fseeko)
14361436
case $host_os in

‎src/backend/storage/ipc/dsm_impl.c‎

Lines changed: 52 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -73,6 +73,7 @@
7373
staticbooldsm_impl_posix(dsm_opop,dsm_handlehandle,Sizerequest_size,
7474
void**impl_private,void**mapped_address,
7575
Size*mapped_size,intelevel);
76+
staticintdsm_impl_posix_resize(intfd,off_tsize);
7677
#endif
7778
#ifdefUSE_DSM_SYSV
7879
staticbooldsm_impl_sysv(dsm_opop,dsm_handlehandle,Sizerequest_size,
@@ -319,7 +320,8 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
319320
}
320321
request_size=st.st_size;
321322
}
322-
elseif (*mapped_size!=request_size&&ftruncate(fd,request_size))
323+
elseif (*mapped_size!=request_size&&
324+
dsm_impl_posix_resize(fd,request_size)!=0)
323325
{
324326
intsave_errno;
325327

@@ -392,7 +394,55 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
392394

393395
return true;
394396
}
395-
#endif
397+
398+
/*
399+
* Set the size of a virtual memory region associated with a file descriptor.
400+
* If necessary, also ensure that virtual memory is actually allocated by the
401+
* operating system, to avoid nasty surprises later.
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*
403+
* Returns non-zero if either truncation or allocation fails, and sets errno.
404+
*/
405+
staticint
406+
dsm_impl_posix_resize(intfd,off_tsize)
407+
{
408+
intrc;
409+
410+
/* Truncate (or extend) the file to the requested size. */
411+
rc=ftruncate(fd,size);
412+
413+
/*
414+
* On Linux, a shm_open fd is backed by a tmpfs file. After resizing with
415+
* ftruncate, the file may contain a hole. Accessing memory backed by a
416+
* hole causes tmpfs to allocate pages, which fails with SIGBUS if there
417+
* is no more tmpfs space available. So we ask tmpfs to allocate pages
418+
* here, so we can fail gracefully with ENOSPC now rather than risking
419+
* SIGBUS later.
420+
*/
421+
#if defined(HAVE_POSIX_FALLOCATE)&& defined(__linux__)
422+
if (rc==0)
423+
{
424+
/* We may get interrupted, if so just retry. */
425+
do
426+
{
427+
rc=posix_fallocate(fd,0,size);
428+
}while (rc==-1&&errno==EINTR);
429+
430+
if (rc!=0&&errno==ENOSYS)
431+
{
432+
/*
433+
* Kernel too old (< 2.6.23). Rather than fail, just trust that
434+
* we won't hit the problem (it typically doesn't show up without
435+
* many-GB-sized requests, anyway).
436+
*/
437+
rc=0;
438+
}
439+
}
440+
#endif/* HAVE_POSIX_FALLOCATE && __linux__ */
441+
442+
returnrc;
443+
}
444+
445+
#endif/* USE_DSM_POSIX */
396446

397447
#ifdefUSE_DSM_SYSV
398448
/*

‎src/include/pg_config.h.in‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -393,6 +393,9 @@
393393
/* Define to 1 if you have the `posix_fadvise' function. */
394394
#undef HAVE_POSIX_FADVISE
395395

396+
/* Define to 1 if you have the `posix_fallocate' function. */
397+
#undef HAVE_POSIX_FALLOCATE
398+
396399
/* Define to 1 if the assembler supports PPC's LWARX mutex hint bit. */
397400
#undef HAVE_PPC_LWARX_MUTEX_HINT
398401

‎src/include/pg_config.h.win32‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -261,6 +261,9 @@
261261
/* Define to 1 if you have the <poll.h> header file. */
262262
/* #undef HAVE_POLL_H */
263263

264+
/* Define to 1 if you have the `posix_fallocate' function. */
265+
/* #undef HAVE_POSIX_FALLOCATE */
266+
264267
/* Define to 1 if you have the `pstat' function. */
265268
/* #undef HAVE_PSTAT */
266269

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