cvs commit: src/sys/kern vfs_bio.c vfs_subr.c src/sys/sys buf.h proc.h src/sys/ufs/ffs ffs_snapshot.c

Christian S.J. Peron csjp at
Thu Sep 29 20:27:12 PDT 2005


On Fri, Sep 30, 2005 at 01:30:02AM +0000, Don Lewis wrote:
> truckman    2005-09-30 01:30:01 UTC
>   FreeBSD src repository
>   Modified files:
>     sys/kern             vfs_bio.c vfs_subr.c 
>     sys/sys              buf.h proc.h 
>     sys/ufs/ffs          ffs_snapshot.c 
>   Log:
>   Un-staticize runningbufwakeup() and staticize updateproc.
>   Add a new private thread flag to indicate that the thread should
>   not sleep if runningbufspace is too large.
>   Set this flag on the bufdaemon and syncer threads so that they skip
>   the waitrunningbufspace() call in bufwrite() rather than than
>   checking the proc pointer vs. the known proc pointers for these two
>   threads.  A way of preventing these threads from being starved for
>   I/O but still placing limits on their outstanding I/O would be
>   desirable.
>   Set this flag in ffs_copyonwrite() to prevent bufwrite() calls from
>   blocking on the runningbufspace check while holding snaplk.  This
>   prevents snaplk from being held for an arbitrarily long period of
>   time if runningbufspace is high and greatly reduces the contention
>   for snaplk.  The disadvantage is that ffs_copyonwrite() can start
>   a large amount of I/O if there are a large number of snapshots,
>   which could cause a deadlock in other parts of the code.
>   Call runningbufwakeup() in ffs_copyonwrite() to decrement runningbufspace
>   before attempting to grab snaplk so that I/O requests waiting on
>   snaplk are not counted in runningbufspace as being in-progress.
>   Increment runningbufspace again before actually launching the
>   original I/O request.
>   Prior to the above two changes, the system could deadlock if enough
>   I/O requests were blocked by snaplk to prevent runningbufspace from
>   falling below lorunningspace and one of the bawrite() calls in
>   ffs_copyonwrite() blocked in waitrunningbufspace() while holding
>   snaplk.
>   See <>
>   Revision  Changes    Path
>   1.495     +3 -3      src/sys/kern/vfs_bio.c
>   1.648     +2 -1      src/sys/kern/vfs_subr.c
>   1.190     +1 -0      src/sys/sys/buf.h
>   1.436     +1 -1      src/sys/sys/proc.h
>   1.104     +16 -4     src/sys/ufs/ffs/ffs_snapshot.c

Christian S.J. Peron
csjp at FreeBSD.ORG
FreeBSD Committer
FreeBSD Security Team

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