lock status of dvp in lookup error return?

Benjamin Kaduk kaduk at MIT.EDU
Wed Oct 19 14:53:52 UTC 2011


On Wed, 19 Oct 2011, Kostik Belousov wrote:

> On Wed, Oct 19, 2011 at 02:07:17AM -0400, Benjamin Kaduk wrote:
>> Hi Rick,
>>
>> In tracking down a panic trying to recursively lock a vnode in openafs, I
>> started questioning my behavior in the ISDOTDOT case, in particular
>> whether to drop the dvp lock before the actual call over the network; this
>> naturally led me to look at the NFS code as a reference.
>> Unfortunately, this left me more confused than when I began ...
>>
>> sys/fs/nfs_clvnops.c, in nfs_lookup():
>>   1211          if (flags & ISDOTDOT) {
>>   1212                  ltype = NFSVOPISLOCKED(dvp);
>>   1213                  error = vfs_busy(mp, MBF_NOWAIT);
>>   1214                  if (error != 0) {
>>   1215                      vfs_ref(mp);
>>   1216                      NFSVOPUNLOCK(dvp, 0);
>>   1217                      error = vfs_busy(mp, 0);
>>   1218                      NFSVOPLOCK(dvp, ltype | LK_RETRY);
>>
>> If we fail to busy the mountpoint, drop the directory lock and try again,
>> then relock dvp afterward.
>>
>>   1219                      vfs_rel(mp);
>>   1220                      if (error == 0 && (dvp->v_iflag & VI_DOOMED)) {
>>   1221                          vfs_unbusy(mp);
>>   1222                          error = ENOENT;
>>   1223                      }
>>   1224                      if (error != 0)
>>   1225                          return (error);
>>
>> But if the second vfs_busy failed, or dvp is DOOMED, return with dvp
>> locked.
>>
>>   1226                  }
>>   1227                  NFSVOPUNLOCK(dvp, 0);
>>
>> But now we always unlock dvp.
>>
>>   1228                  error = nfscl_nget(mp, dvp, nfhp, cnp, td, &np,
>>   NULL,
>>   1229                      cnp->cn_lkflags);
>>
>> The call to the network (?)
>>
>>   1230                  if (error == 0)
>>   1231                      newvp = NFSTOV(np);
>>   1232                  vfs_unbusy(mp);
>>   1233                  if (newvp != dvp)
>>   1234                      NFSVOPLOCK(dvp, ltype | LK_RETRY);
> Did you missed line 1234 ?
>
> The code is the copy of the vn_vget_ino(). The logic in the function
> might be slightly easier to follow.

Ah, I did miss that, thanks.
Maybe 0200h is not the best time to do these things ...

-Ben


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