Messages in this thread | | | Date | Mon, 11 May 2009 01:58:23 +0200 | From | Ulrich Lukas <> | Subject | whole system lock-up on low memory |
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Hi,
vanilla linux 2.6.29.3, AMD64, tested on openSUSE 11.1 and Kubuntu 9.04.
I observe the following behaviour:
When any user application (non-kernel, non-root) consumes all the available system memory, the system freezes completely instead of any application being killed by the oom-killer.
The mouse pointer stalls, and there is a seemingly endless loop of hard-disc access, even when no swap space on any harddisc is activated.
IMO, this is severe, because any application can practically crash the system (e.g. in case of a memory-leak), causing data loss in case of unsaved data.
To reproduce this, I've attached a small C++ utility (compiles with g++ memory_overcommit.cc -o memory_overcommit.bin) which allocates chunks of memory of user defined size.
On the Ubuntu system, the system freeze can be observed with swap enabled on a cryptographic swap partition (dm-crypt; /etc/crypttab). With openSUSE the lock-up also occurs with deactivated swap. (swapoff -a).
Tested from a KDE terminal window as regular urser, the steps to reproduce are:
* use cryptographic swap partition or disable swap (maybe also reproducible with normal swap; but apparently not on Suse)
* compile and invoke the attached code: ./memory_overcommit.bin
* enter a number (in MiB) of memory that is slightly smaller than the available memory and press "enter" key once.
* enter a smaller number (minimum 1 MiB) and confirm again, do the same again,..., successively approaching the limit of available memory with smaller chunks.
* finally, when most of the memory/buffers/cache are used-up, the system becomes unresponsive and constant, heavy harddisk-access commences.
Sometimes, killing the X-server or shutting down via hotkeys works after several minutes of waiting, but this is not consistent.
I've reported this issue on the Ubuntu bug tracker before: https://bugs.launchpad.net/ubuntu/+bug/283420
but as stated above, I also had the problem on another system.
I'd be glad if I could help if you need further information.
Attachement: one file, memory_overcommit.cc (also here: http://datenparkplatz.de/DiesUndDas/memory_overcommit.cc) --- #include <cassert> #include <cerrno> #include <clocale> #include <cstdio> #include <cstdlib> #include <cstring> #include <limits>
using std::exit; using std::numeric_limits; using std::printf; using std::size_t; using std::strlen;
void read_answer(char* buffer, size_t buffer_size) { assert(buffer_size > 1);
char const* ret = std::fgets(buffer, buffer_size, stdin); if(ret == 0) { printf("\nSorry, there was an error while reading the answer. This program will now terminate.\n");
exit(EXIT_FAILURE);
}
else if(strlen(buffer) == buffer_size - 1 && buffer[buffer_size - 2] != '\n') {
printf("Sorry, you answer is too long (possibly out of range). This program will now terminate.\n");
exit(EXIT_FAILURE);
}
}
size_t determine_size(char const* s) { assert(strlen(s) > 0);
char* endptr = 0; errno = 0; unsigned long v = std::strtoul(s, &endptr, 10); if(strlen(s) == 1 || endptr != s + strlen(s) - 1) { printf("\nSorry, your answer does not appear to be valid. This program will now terminate.\n");
exit(EXIT_FAILURE);
}
else if((v == numeric_limits<unsigned long>::max() && errno == ERANGE) || v == 0 || numeric_limits<unsigned long>::max() / (1024 * 1024) < v) {
printf("\nSorry, that value is out of range. This program will now terminate.\n"); exit(EXIT_FAILURE);
}
v *= 1024 * 1024;
assert(numeric_limits<size_t>::is_specialized); if(v > numeric_limits<size_t>::max() ) { printf("\nSorry, that value is out of range. This program will now terminate.\n"); exit(EXIT_FAILURE);
}
return v; }
bool inquire_repeat(size_t& v) { printf("\nShould a new allocation be made? You can enter:\n" "==> \"No\" to quit,\n" "==> Any Number of MiB to change the chunk size and continue, or\n" "==> Hit return to continue with last chunk size.\n\nYour answer: ");
char answer[20]; read_answer(answer, sizeof(answer) ); if(std::strcmp(answer, "\n") == 0) { return true; } else if(std::strcmp(answer, "No\n") == 0) { return false; }
v = determine_size(answer); return true; }
int main() { #ifdef _POSIX_C_SOURCE std::setlocale(LC_ALL, ""); // Prepare thousands grouping in output. #endif
printf("\n\nThis program allows to repeatedly allocate chunks of memory of user-specified size. " "\nAfter each allocation the user can choose to repeat or to quit the program.\n\nFirst, please enter now "
"the amount of memory in MiB (1024 * 1024 bytes) \nto allocate in each round: "); char answer[20];
read_answer(answer, sizeof(answer) );
size_t alloc_size = determine_size(answer);
size_t total = 0; do { printf("\n >>> Starting to allocate chunk...\n"); std::fflush(stdout); void* p = std::malloc(alloc_size); if(!p) { printf("\n > The last memory allocation failed." "\n > This means the system reported the out-of-memory condition orderly." "\nThis program will now terminate.\n");
exit(0);
}
std::memset(p, 0, alloc_size);
printf(" >>> A chunk was just allocated! <<<\n"); if(numeric_limits<size_t>::max() - total >= alloc_size) { total += alloc_size;
#ifdef _POSIX_C_SOURCE char const* fmt_string = " The total number of bytes allocated is now %'zu.\n"; #else char const* fmt_string = " The total number of bytes allocated is now %zu.\n"; #endif
printf(fmt_string, total); } else { #ifdef _POSIX_C_SOURCE char const* fmt_string = " More than %'zu bytes have been allocated in total by now.\n"; #else char const* fmt_string = " More than %zu bytes have been allocated in total by now.\n"; #endif
printf(fmt_string, total); total = numeric_limits<size_t>::max(); } } while(inquire_repeat(alloc_size) );
printf("\nQuit was requested. This program will now terminate.\n"); }
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