Hi, Thank you for your kind comments. I'm still discussing the answer with my senior colleagues, so please wait a few days. I think I can reply at the beginning of next week.
Best regards, -- Hidehiro Kawai Hitachi, Ltd., Systems Development Laboratory Andrew Morton wrote: > On Fri, 02 Mar 2007 13:41:30 +0900 > "Kawai, Hidehiro" <[EMAIL PROTECTED]> wrote: > > >>This patch series is version 4 of the core dump masking feature, >>which provides a per-process flag not to dump anonymous shared >>memory segments. > > > First up, please convince us that this problem cannot be solved in > userspace. Note that we now support dumping core over a pipe to a > userspace application which can perform filtering such as this (see > Documentation/sysctl/kernel.txt:core_pattern). > > > Assuming that your argument is successful... > > - The unpleasing trylock in proc_coredump_omit_anon_shared_write() is > there, I believe, to handle the case where a coredump is presently in > progress. We don't want to change the filtering rule while the dump is > happening. > > What I suggest you do instead is to take a copy of > mm->coredump_omit_anon_shared into a local variable with one single read > per coredump. Pass that local down into all the callees which need to > see it. That way, no locking is needed. > > - These games we're playing with the atomicity of the bitfields in the > mm_struct need to go away. > > First up, please prepare a standalone patch which removes > mm_struct.dumpable and adds `unsigned long mm_struct.flags'. Include a > comment telling people that they must use atomic bitops (set_bit, > clear_bit) on > mm_struct.flags. > > Reimplement the current three-value dumpable silliness using two or > three separate flags in mm_struct.flags. Of course, this design means > that there will be tiny timing windows where the value of these two or > three flags have intermediate, invalid states. Please take care of those > little windows and document how you did so. I expect a suitable approach > would be to set and clear the flags in a suitable order, so that if a > race _does_ happen, the results are benign. > > - Once that is done, you're ready to think about your new functionality. > Start out with > > #define MM_FLAG_COREDUMP_OMIT_ANON_SHARED (1 << 3) > > or whatever, and it all becomes easy. > > - Finally, the code as you have it here is very specific to your specific > requirement: don't dump shared memory segments. > > But if we're going to implement in-kernel core-dump filtering of this > nature, we should design it extensibly, even if we don't actually > implement those extensions at this time. > > Because other people might (reasonably) wish to omit anonymous memory, > or private mappings, or file-backed VMAs, or whatever. > > So maybe /proc/pid/coredump_omit_anon_shared should become > /proc/pid/core_dumpfilter, which is a carefully documented bitmask. > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
