From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 4 Jul 1999 19:38:26 +0200 (CEST) From: Andrea Arcangeli Subject: Re: [patch] fix for OOM deadlock in swap_in (2.2.10) [Re: [test program] for OOM situations ] In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Rik van Riel , Bernd Kaindl , Linux Kernel , kernel@suse.de, linux-mm@kvack.org, Alan Cox List-ID: On Sun, 4 Jul 1999, Linus Torvalds wrote: >Andreas patch has a much more serious problem: it changes accepted UNIX >semantics. Try this before and after the patch: > >#include >#include >#include > >#define PAGE_SIZE 4096 > >int main(int argc, char **argv) >{ > int fd; > char * map; > > fd = open("/tmp/duh", O_RDWR | O_CREAT, 0666); > if (fd < 0) > exit(1); > ftruncate(fd, PAGE_SIZE); > map = mmap(NULL, PAGE_SIZE*2, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); > *(volatile char *)(map+PAGE_SIZE); > return 0; >} On stock 2.2.10: andrea@black:~$ strace ./a.out execve("./a.out", ["./a.out"], [/* 24 vars */]) = 0 brk(0) = 0x804a69c open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = 3 fstat(3, {st_mode=0, st_size=0, ...}) = 0 mmap(0, 6184, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000c000 close(3) = 0 open("/lib/libc.so.6", O_RDONLY) = 3 mmap(0, 4096, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000e000 munmap(0x4000e000, 4096) = 0 mmap(0, 672848, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x4000e000 mprotect(0x400a0000, 74832, PROT_NONE) = 0 mmap(0x400a0000, 28672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x91000) = 0x400a0000 mmap(0x400a7000, 46160, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x400a7000 close(3) = 0 personality(PER_LINUX) = 0 getpid() = 130 open("/tmp/duh", O_RDWR|O_CREAT, 0666) = 3 ftruncate(3, 4096) = 0 mmap(0, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x400b3000 --- SIGBUS (Bus error) --- +++ killed by SIGBUS +++ On 2.2.10 + my oom patch: andrea@black:~$ strace ./a.out execve("./a.out", ["./a.out"], [/* 24 vars */]) = 0 brk(0) = 0x804a69c open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = 3 fstat(3, {st_mode=0, st_size=0, ...}) = 0 mmap(0, 6184, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000c000 close(3) = 0 open("/lib/libc.so.6", O_RDONLY) = 3 mmap(0, 4096, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000e000 munmap(0x4000e000, 4096) = 0 mmap(0, 672848, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x4000e000 mprotect(0x400a0000, 74832, PROT_NONE) = 0 mmap(0x400a0000, 28672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x91000) = 0x400a0000 mmap(0x400a7000, 46160, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x400a7000 close(3) = 0 personality(PER_LINUX) = 0 getpid() = 131 open("/tmp/duh", O_RDWR|O_CREAT, 0666) = 3 ftruncate(3, 4096) = 0 mmap(0, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x400b3000 --- SIGBUS (Bus error) --- +++ killed by SIGBUS +++ >and see the difference.. I can't see differences: andrea@black:~$ diff 2.2.10 2.2.10- 17c17 < getpid() = 134 --- > getpid() = 128 >And Andrea, I told you this once already in private email. I told you why. Yes, the first patch I sent to you privately some week ago was plain buggy (I wasn't aware of the shared-mmap-sigbugs UNIX semantic). And I really thank you very much for have spent some time teaching me why it was buggy. >Why don't you listen? "Fixing" a bug badly is worse than leaving it as a >known bug. I think I listen, I remeber well your emails. I written the new patch with your emails in mind. Now I send a sigbus and _nothing_ more when somebody access beyond the end of the file in a shared mmap. The first patch I sent you some time ago was buggy since I replaced the sigbus with a sigkill in do_page_fault, but now I force the signals only at the lower level (as shm and other places was just doing) and the retval of handle_mm_fault now _only_ tells do_page_fault if it has to fixup or not. Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/