[Bug runtime/27881] New: failed to extend vma mapped entry when the address is adjacent

[Bug runtime/27881] New: failed to extend vma mapped entry when the address is adjacent

[zhuizhuhaomeng at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

            Bug ID: 27881
           Summary: failed to extend vma mapped entry when the address is
                    adjacent
           Product: systemtap
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: zhuizhuhaomeng at gmail dot com
  Target Milestone: ---

[root@centos7-cube agentzh]# cat /proc/7877/maps | grep nginx
5579ad030000-5579ad067000 r--p 00000000 fd:00 54825380                  
/usr/local/openresty-plus/nginx/sbin/nginx
5579ad067000-5579ad180000 r-xp 00037000 fd:00 54825380                  
/usr/local/openresty-plus/nginx/sbin/nginx
5579ad180000-5579ad1ce000 r--p 00150000 fd:00 54825380                  
/usr/local/openresty-plus/nginx/sbin/nginx
5579ad1cf000-5579ad1d1000 r--p 0019e000 fd:00 54825380                  
/usr/local/openresty-plus/nginx/sbin/nginx
5579ad1d1000-5579ad1ef000 rw-p 001a0000 fd:00 54825380                  
/usr/local/openresty-plus/nginx/sbin/nginx



the first two segments are adjacent but stap did not extend the second to the
first. Instead, stap add two entries.  entry_2, entry_1 in the list with
hlist_add_head_rcu.

the third，fourth ，fifth segments were not added because they can not match the
if condition below. 




                          if (res == -ESRCH || vm_start + offset == addr)
                            res = stap_add_vma_map_info(tsk->group_leader,
                                                        addr, addr + length,
                                                        offset, path, module);
                          else if (res == 0 && vm_end + 1 == addr)
                            res = stap_extend_vma_map_info(tsk->group_leader,
                                                           vm_start,
                                                           addr + length);


when access a global variable，_stp_umodule_relocate will use the entry_2's
vm_start as base address. actually, should use the first entry's vm_start as
the base address.


    if (stap_find_vma_map_info_user(tsk->group_leader, m,
                                    &vm_start, NULL, NULL) == 0) {
      offset += vm_start;
      dbug_sym(1, "address=%lx\n", offset);
      return offset;
    } 


when get the relative address in _stp_kallsyms_lookup, we should also use the
first entry's vm_start as the base address.

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[zhuizhuhaomeng at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

--- Comment #1 from lijunlong <zhuizhuhaomeng at gmail dot com> ---
Created attachment 13461
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13461&action=edit
vma user module mapped entries

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[zhuizhuhaomeng at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

--- Comment #2 from lijunlong <zhuizhuhaomeng at gmail dot com> ---
The patch is here. Added an attachment also.

diff --git a/runtime/task_finder_vma.c b/runtime/task_finder_vma.c
index 17aaec386..fc388aaf2 100644
--- a/runtime/task_finder_vma.c
+++ b/runtime/task_finder_vma.c
@@ -54,7 +54,7 @@ struct __stp_tf_vma_entry {
        struct task_struct *tsk;
        unsigned long vm_start;
        unsigned long vm_end;
-       unsigned long offset;
+       unsigned long offset;  //offset from base addr of the module
        char path[TASK_FINDER_VMA_ENTRY_PATHLEN]; /* mmpath name, if known */

        // User data (possibly stp_module)
@@ -243,7 +243,7 @@ stap_add_vma_map_info(struct task_struct *tsk, unsigned
long vm_start,
        }

        stp_spin_lock_irqsave(&bucket->lock, flags);
-       hlist_add_head_rcu(&entry->hlist, &bucket->head);
+       hlist_add_tail_rcu(&entry->hlist, &bucket->head);
        stp_spin_unlock_irqrestore(&bucket->lock, flags);
        return 0;
 }
@@ -303,7 +303,7 @@ stap_find_vma_map_info(struct task_struct *tsk, unsigned
long addr,

        bucket = __stp_tf_get_vma_bucket(tsk);
        entry = __stp_tf_get_vma_map(bucket, tsk, 1, addr >= entry->vm_start &&
-                                    addr < entry->vm_end);
+                                    addr <= entry->vm_end);
        if (!entry)
                return -ESRCH;

diff --git a/runtime/vma.c b/runtime/vma.c
index 2bf1b0a9c..78623fda3 100644
--- a/runtime/vma.c
+++ b/runtime/vma.c
@@ -185,14 +185,15 @@ static int _stp_vma_mmap_cb(struct
stap_task_finder_target *tgt,
                                                            module,
                                                            &vm_start, &vm_end,
                                                            NULL);
-                         if (res == -ESRCH || vm_start + offset == addr)
+                         if (res == -ESRCH)
                            res = stap_add_vma_map_info(tsk->group_leader,
-                                                       addr, addr + length,
-                                                       offset, path, module);
-                         else if (res == 0 && vm_end + 1 == addr)
-                           res = stap_extend_vma_map_info(tsk->group_leader,
-                                                          vm_start,
-                                                          addr + length);
+                                                       addr, addr + length,
+                                                       0, path, module);
+                         else
+                           res = stap_add_vma_map_info(tsk->group_leader,
+                                                       addr, addr + length,
+                                                       addr - vm_start, path,
module);
+
                          /* VMA entries are allocated dynamically, this is
fine,
                           * since we are in a task_finder callback, which is
in
                           * user context. */

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[zhuizhuhaomeng at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

--- Comment #3 from lijunlong <zhuizhuhaomeng at gmail dot com> ---
Created attachment 13464
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13464&action=edit
fixed coding style

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[zhuizhuhaomeng at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

--- Comment #4 from lijunlong <zhuizhuhaomeng at gmail dot com> ---
I have updated the patch to fix coding style.

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[scox at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

Stan Cox <scox at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-05-27
     Ever confirmed|0                           |1
                 CC|                            |scox at redhat dot com
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #5 from Stan Cox <scox at redhat dot com> ---
An alternate hlist_add_tail_rcu needs to be provided for those kernels that
don't have it.

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[Bug runtime/27881] failed to extend vma mapped entry when the address is adjacent

[scox at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27881

Stan Cox <scox at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|systemtap at sourceware dot org    |scox at redhat dot com

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