Messages in this thread | | | Date | Thu, 16 May 2002 19:27:59 +0200 | From | Andi Kleen <> | Subject | Re: PATCH Multithreaded core dump support for the 2.5.14 (and 15) kernel. |
| |
On Thu, May 16, 2002 at 10:13:40AM -0400, Mark Gross wrote: > Also, does anyone know WHY the mmap_sem is needed in the elf_core_dump code, > and is this need still valid if I've suspended all the other processes that > could even touch that mm? I.e. can I fix this by removing the down_write / > up_write in elf_core_dump?
The mmap_sem is needed to access current->mm (especially the vma list) safely. Otherwise someone else sharing the mm_struct could modify it. If you make sure all others sharing the mm_struct are killed first (including now way for them to start new clones inbetween) then the only loophole left would be remote access using /proc/pid/mem or ptrace. If you handle that too then it is probably safe to drop it. Unfortunately I don't see a way to handle these remote users without at least taking it temporarily.
Of course there are other semaphores in involved in dumping too (e.g. the VFS ->write code may take the i_sem or other private ones). I guess they won't be a big problem if you first kill and then dump later.
-Andi
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |