[LU-17793] warning: objtool: __cfs_fail_check_set() falls through to next function __cfs_fail_timeout_set()

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Affects Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Jian Yu
• Reporter: Jian Yu

Description

While building master branch on Ubuntu 24.04 with kernel 6.8.0-31-generic, there are lots of objtool warnings as follows:

  CC [M]  /root/lustre-release/libcfs/libcfs/fail.o
/root/lustre-release/libcfs/libcfs/fail.o: warning: objtool: __cfs_fail_check_set() falls through to next function __cfs_fail_timeout_set()
  CC [M]  /root/lustre-release/libcfs/libcfs/module.o
/root/lustre-release/libcfs/libcfs/module.o: warning: objtool: libcfs_force_lbug() falls through to next function debugfs_doint()
  CC [M]  /root/lustre-release/libcfs/libcfs/tracefile.o
  CC [M]  /root/lustre-release/libcfs/libcfs/libcfs_string.o
  CC [M]  /root/lustre-release/libcfs/libcfs/hash.o
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_bd_del_locked() falls through to next function cfs_hash_cond_del_locked()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_bd_from_key() falls through to next function cfs_hash_buckets_free()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_bd_get() falls through to next function cfs_hash_multi_bd_findadd_locked.constprop.0()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_create() falls through to next function cfs_hash_bd_move_locked()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_bd_move_locked() falls through to next function cfs_hash_rehash_worker()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_dual_bd_get() falls through to next function cfs_hash_rehash_key()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_rehash_cancel() falls through to next function cfs_hash_putref()
/root/lustre-release/libcfs/libcfs/hash.o: warning: objtool: cfs_hash_for_each_enter() falls through to next function cfs_hash_rehash()

A full list is in the attached make_debs.log.
According to https://github.com/torvalds/linux/blob/master/tools/objtool/Documentation/objtool.txt :

8. file.o: warning: objtool: funcA() falls through to next function funcB()

   This means that funcA() doesn't end with a return instruction or an
   unconditional jump, and that objtool has determined that the function
   can fall through into the next function.  There could be different
   reasons for this:

   1) funcA()'s last instruction is a call to a "noreturn" function like
      panic().  In this case the noreturn function needs to be added to
      objtool's hard-coded global_noreturns array.  Feel free to bug the
      objtool maintainer, or you can submit a patch.

   2) funcA() uses the unreachable() annotation in a section of code
      that is actually reachable.

   3) If funcA() calls an inline function, the object code for funcA()
      might be corrupt due to a gcc bug.  For more details, see:
      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646

Issue Links

• is related to: LU-17540 sync and delay before LBUG() calls panic()
• is related to: LU-8130 Migrate from libcfs hash to rhashtable