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From Greg Ames <grega...@remulak.net>
Subject mod_include seg faults
Date Fri, 21 Sep 2001 20:18:17 GMT
(sigh...where did I put the phone # for the mod_include help desk?) 

With a cvs checkout from Wednesday PM on daedalus, I get seg faults in
ap_save_brigade() called by send_parsed_content() in mod_include.c .
We've seen the URL before - http://httpd.apache.org/docs/misc/FAQ.html
.  The same request works fine on my Linux box.

We appear to be processing the <!--#include virtual="FAQ-D.html?" -->
tag.  The brigade passed into ap_save_brigade() starts with a valid MMAP
bucket, followed by trash which may be a sentinel for another brigade. 
This is right after a split, and the other brigade from the split looks
bad too.  I don't see any signs of network errors.

Since I have no idea where the brigades got trashed, my plan is to
create a debug function which walks its input brigade and verifies that
each bucket has a valid type field, then sprinkle calls to this function
in strategic places within send_parsed_content().  Other ideas are
appreciated.

Questions:

* Since this code seems pretty fragile, I'm wondering if I should wrap
my debug code in #ifdef DEBUG_INCLUDE logic and commit it, assuming it
shakes out the current bug?

* Looking thru the commit logs, I see hundreds of lines of changes going
in since 2.0.25, when I believe it worked.  I don't think any of these
changes have simplified the module, and it was pretty complex to start
with.  About a year ago, I remember rbb commenting that this code needed
rewriting.  Now I'm a believer.  What can we do to simplify this code? 
Use a char * variable to hold the current tag?

Opinions?  

Greg

------------------------------------------------------------

a few details from the dump.  If you want more, the dump is on daedalus
at /usr/local/apache2.0.26-dev/corefiles/httpd.core . 

(gdb) bt
#0  0x806dce3 in ap_save_brigade (f=0x8247c9c, saveto=0x8264054,
b=0xbfbfacc8,
    p=0x824700c) at util_filter.c:296
#1  0x281e2abd in send_parsed_content (bb=0xbfbfb13c, r=0x824703c,
f=0x8247c9c)     at mod_include.c:2960
#2  0x281e2e54 in includes_filter (f=0x8247c9c, b=0x8247e4c)
    at mod_include.c:3094
[...]
(gdb) fr 1
#1  0x281e2abd in send_parsed_content (bb=0xbfbfb13c, r=0x824703c,
f=0x8247c9c)
    at mod_include.c:2960
 
2960                ap_save_brigade(f, &ctx->ssi_tag_brigade,
&tag_and_after, r->pool);
(gdb) list
2955                                           
APR_BUCKET_NEXT(ctx->head_start_bucket);
2956                    ctx->head_start_index = 0;
2957                }
2958                               /* Set aside tag, pass pre-tag... */
2959                tag_and_after = apr_brigade_split(*bb,
ctx->head_start_bucket);
2960                ap_save_brigade(f, &ctx->ssi_tag_brigade,
&tag_and_after, r->pool);
2961                rv = ap_pass_brigade(f->next, *bb);
2962                if (rv != APR_SUCCESS) {
2963                    return rv;
2964                }
(gdb) dump_brigade tag_and_after
dump of brigade 0x8247e7c
   0: bucket=MMAP(0x8100440), length=187, data=0x80e8080
   1Cannot access memory at address 0x0.
(gdb) p *tag_and_after
$1 = {p = 0x824700c, list = {next = 0x8100440, prev = 0x8247e50}}
(gdb) p *tag_and_after.list.next
$3 = {link = {next = 0x8247e30, prev = 0x8247e80}, type = 0x280b0fd4,
  length = 187, start = 18504, data = 0x80e8080, sms = 0x80e4000}
(gdb) p *tag_and_after.list.next.link.next
$4 = {link = {next = 0x8247e50, prev = 0x8100440}, type = 0x0,
  length = 136609324, start = 2885267100644575012, data = 0x8247dcc,
  sms = 0x824700c}

(gdb) dump_brigade *bb
dump of brigade 0x8247e4c
   0Cannot access memory at address 0x0.
(gdb) p *bb
$6 = (apr_bucket_brigade *) 0x8247e4c
(gdb) p **bb
$7 = {p = 0x824700c, list = {next = 0x8247e80, prev = 0x8247e30}}
(gdb) p *(**bb).list.next
$10 = {link = {next = 0x8100440, prev = 0x8247e50}, type = 0x0,
  length = 136609404, start = 2885267100644575012, data = 0x8247e5c, sms
= 0x0}

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