Re: [Crash-utility] [PATCH] Fix for some command-line cases an unintended unlink of a file crash didn't create and a leftover temporary

Hi Dave, On 06/13/2014 12:55 PM, Dave Anderson wrote: > > > ----- Original Message ----- >> >> >> ----- Original Message ----- >>> When the crash command line includes two filenames where one is a >>> compressed kernel and the other is a debuginfo file and they appear in >>> that order then if the uncompressed temporary version of the kernel is >>> actually larger than the debuginfo then crash will end with an error but >>> will also unlink the debuginfo file and will not clean up the (intended >>> temporary) uncompressed copy of the kernel. >> >> Hi Dave, >> >> It's taken me awhile to wrap my head around this, but my first question is: >> how is it possible that the uncompressed stripped kernel can possibly be >> larger than the debuginfo file? >> >> I only have old RHEL3 kernels as examples, but the .debug versions >> of the kernel are 5 to 6 times larger than the stripped kernel. >> >>> This patch at least fixes the unintended unlink and leaving the >>> temporary present. It doesn't fix the failure to start but that's >>> because the wrong files are assumed the debuginfo and kernel. The size >>> case that led to this discovery is probably rare. >> >> Is the unintended unlink() done in the first display_sys_stats() or >> in clean_exit()? >> >> And then with your fix applied, why does the crash session still fail? >> >> Dave > > Hi Dave, > > Although I'm still interested in answers to the questions above, this > patch also fixes a different scenario. > > In testing the 8 possible combinations using RHEL3 vmlinux/vmlinux.gz > and vmlinux.debug/vmlinux.debug.gz files, I found that I could reproduce > the problem with this particular combination/order: > > $ crash vmlinux.debug.gz vmlinux ... > > Similar to your setup, the pc->namelist_orig field continues to > be non-NULL, and therefore pc->namelist (vmlinux) gets removed in > clean_exit(), and since pc->namelist_debug_orig doesn't get set, > the uncompressed temporary debug file remains! Yes, vmlinux.gz passes is_compressed_kernel() and there is a tmpname (vmlinux.debug_XXXXXX with unique name replacement of XXXXXX). select_namelist() gets called with tmpname (as the argument new) and all the namelist values in pc are NULL. select_namelist() uses new to set pc->namelist (to vmlinux.debug_XXXXXX). On return to main(), pc->namelist_orig gets set to argv[optind] (vmlinux.debug.gz).

argv[optind] = vmlinux.debug.gz // State before select_namelist() pc->namelist is NULL pc->namelist_orig is NULL pc->namelist_debug is NULL pc->namelist_debug_orig is NULL select_namelist(vmlinux.debug_XXXXXX) // State shortly after select_namelist() pc->namelist is vmlinux.debug_XXXXXX pc->namelist_orig is vmlinux.debug.gz pc->namelist_debug is NULL pc->namelist_debug_orig is NULL The next argument, vmlinux, passes is_kernel() and select_namelist() gets called with argv[optind] (as the argument new). Since there is a namelist value already select_namelist() gets the struct stat for each file (vmlinux.debug_XXXXXX and vmlinux, the first is a larger file). select_namelist() copies pc->namelist (vmlinux.debug_XXXXXX) to pc->namelist_debug and sets pc->namelist from new (vmlinux) leaving pc->namelist_orig set to vmlinux.debug.gz and pc->namelist_debug_orig as NULL. argv[optind] = vmlinux // State before select_namelist() pc->namelist is vmlinux.debug_XXXXXX pc->namelist_orig is vmlinux.debug.gz pc->namelist_debug is NULL pc->namelist_debug_orig is NULL select_namelist(vmlinux) // State shortly after select_namelist() pc->namelist is vmlinux pc->namelist_orig is vmlinux.debug.gz pc->namelist_debug is vmlinux.debug_XXXXXX pc->namelist_debug_orig is NULL That leaves namelist_debug with no indication it is an uncompressed, temporary file (the equivalent _orig member of pc is NULL) and indicates vmlinux is an uncompressed temporary file (the equivalent _orig member of pc is non-NULL) when clean_exit() is used so there is an unintended unlink of vmlinux and an uncleaned vmlinux.debug_XXXXXX temporary. > Nice fix! Thanks, I'm glad to help. -- David. > >> >> >>> The cause is that evidence of a temporary file to unlink is that there >>> is a value in pc->namelist and pc->namelist_orig (or pc->namelist_debug >>> and pc->namelist_orig_debug) but when the file size test in >>> select_namelist() results in the pc->namelist copy to pc->namelist_debug >>> the _orig is not copied as well so the implied file to unlink is the one >>> set in pc->namelist (the debuginfo filename now). >>> >>> The patch causes a populated namelist_orig value to be swapped with >>> namelist_debug_orig if the namelist value is copied to namelist_debug. >>> >>> Signed-off-by: David Mair <dmair(a)suse.com&gt; >>> --- >>> symbols.c | 7 +++++++ >>> 1 file changed, 7 insertions(+) >>> >>> diff --git a/symbols.c b/symbols.c >>> index 4c6fbf4..e1ed719 100644 >>> --- a/symbols.c >>> +++ b/symbols.c >>> @@ -3520,6 +3520,7 @@ int >>> select_namelist(char *new) >>> { >>> struct stat stat1, stat2; >>> + char *namecp; >>> >>> if (pc->server_namelist) { >>> pc->namelist_debug = new; >>> @@ -3533,6 +3534,12 @@ select_namelist(char *new) >>> >>> if (stat1.st_size > stat2.st_size) { >>> pc->namelist_debug = pc->namelist; >>> + if (pc->namelist_orig) >>> + { >>> + namecp = pc->namelist_debug_orig; >>> + pc->namelist_debug_orig = pc->namelist_orig; >>> + pc->namelist_orig = namecp; >>> + } >>> pc->namelist = new; >>> } else if (stat2.st_size > stat1.st_size) >>> pc->namelist_debug = new; >>> >>> -- >>> Crash-utility mailing list >>> Crash-utility(a)redhat.com >>> https://www.redhat.com/mailman/listinfo/crash-utility >>> >> >> -- >> Crash-utility mailing list >> Crash-utility(a)redhat.com >> https://www.redhat.com/mailman/listinfo/crash-utility >> > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility > -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility