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Fix a race between the syncer and umount. When you umount a softupdates 

filesystem softdep_process_worklist() is called in a loop until it indicates
that no dependancies remain, but the determination of that fact depends on
there only being one softdep_process_worklist() instance running.  It was
possible for the syncer to also be running softdep_process_worklist()
and the pre-existing checks in the code to prevent this were not sufficient
to prevent the race.  This patch solves the problem.

Approved-by: mckusick
This commit is contained in:
Matthew Dillon 2001-01-30 06:31:59 +00:00
parent 209a653f29
commit f8e071a1eb
1 changed files with 38 additions and 12 deletions
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50
sys/ufs/ffs/ffs_softdep.c
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@ -439,6 +439,7 @@ workitem_free(item, type)
static struct workhead softdep_workitem_pending;
static int num_on_worklist; /* number of worklist items to be processed */
static int softdep_worklist_busy; /* 1 => trying to do unmount */
static int softdep_worklist_req; /* serialized waiters */
static int max_softdeps; /* maximum number of structs before slowdown */
static int tickdelay = 2; /* number of ticks to pause during slowdown */
static int proc_waiting; /* tracks whether we have a timeout posted */
@ -526,14 +527,19 @@ softdep_process_worklist(matchmnt)
*/
filesys_syncer = p;
matchcnt = 0;
/*
* There is no danger of having multiple processes run this
* code. It is single threaded solely so that softdep_flushfiles
* (below) can get an accurate count of the number of items
* code, but we have to single-thread it when softdep_flushfiles()
* is in operation to get an accurate count of the number of items
* related to its mount point that are in the list.
*/
if (softdep_worklist_busy && matchmnt == NULL)
return (-1);
if (matchmnt == NULL) {
if (softdep_worklist_busy < 0)
return(-1);
softdep_worklist_busy += 1;
}
/*
* If requested, try removing inode or removal dependencies.
*/
@ -551,8 +557,16 @@ softdep_process_worklist(matchmnt)
starttime = time_second;
while (num_on_worklist > 0) {
matchcnt += process_worklist_item(matchmnt, 0);
if (softdep_worklist_busy && matchmnt == NULL)
return (-1);
/*
* If a umount operation wants to run the worklist
* accurately, abort.
*/
if (softdep_worklist_req && matchmnt == NULL) {
matchcnt = -1;
break;
}
/*
* If requested, try removing inode or removal dependencies.
*/
@ -577,8 +591,15 @@ softdep_process_worklist(matchmnt)
* second. Otherwise the other syncer tasks may get
* excessively backlogged.
*/
if (starttime != time_second && matchmnt == NULL)
return (-1);
if (starttime != time_second && matchmnt == NULL) {
matchcnt = -1;
break;
}
}
if (matchmnt == NULL) {
softdep_worklist_busy -= 1;
if (softdep_worklist_req && softdep_worklist_busy == 0)
wakeup(&softdep_worklist_req);
}
return (matchcnt);
}
@ -710,11 +731,14 @@ softdep_flushworklist(oldmnt, countp, p)
int count, error = 0;
/*
* Await our turn to clear out the queue.
* Await our turn to clear out the queue, then serialize access.
*/
while (softdep_worklist_busy)
tsleep(&lbolt, PRIBIO, "softflush", 0);
softdep_worklist_busy = 1;
while (softdep_worklist_busy) {
softdep_worklist_req += 1;
tsleep(&softdep_worklist_req, PRIBIO, "softflush", 0);
softdep_worklist_req -= 1;
}
softdep_worklist_busy = -1;
/*
* Alternately flush the block device associated with the mount
* point and process any dependencies that the flushing
@ -732,6 +756,8 @@ softdep_flushworklist(oldmnt, countp, p)
break;
}
softdep_worklist_busy = 0;
if (softdep_worklist_req)
wakeup(&softdep_worklist_req);
return (error);
}