code: plan9front

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gefs: fix deadlock between epochclean and truncwait

epochclean should not hold the mutation lock, which
should allow procs within an epoch to make progress
and end their epoch.

--- a/sys/src/cmd/gefs/fs.c

+++ b/sys/src/cmd/gefs/fs.c

@@ -2353,8 +2353,8 @@

 		}

 		assert(estacksz() == 0);

 		epochend(id);

-		epochclean();

 		qunlock(&fs->mutlk);

+		epochclean();

 		if(a != nil)

 			chsend(fs->admchan, a);

@@ -2396,8 +2396,8 @@

 			bp = unpackbp(kv.v, kv.nv);

 			freetree(bp, pred);

 			qlock(&fs->mutlk);

-			epochclean();

 			qunlock(&fs->mutlk);

+			epochclean();

 		}

 	}

 	if(rb.gen > pred)

@@ -2432,8 +2432,8 @@

 		if(bp.gen > t->pred)

 			freebp(nil, bp);

 		qlock(&fs->mutlk);

-		epochclean();

 		qunlock(&fs->mutlk);

+		epochclean();

 	}

 	btexit(&s);

 	freetree(t->bp, t->pred);

@@ -2445,12 +2445,12 @@

 	char buf[Kvmax];

 	Msg mb[Kvmax/Offksz];

 	Bptr bp, nb, *oldhd;

+	int i, nm;

 	vlong off;

 	Tree *t;

 	Arena *a;

 	Amsg *am;

 	Blk *b;

-	int i, nm;

 	if((oldhd = calloc(fs->narena, sizeof(Bptr))) == nil)

 		sysfatal("malloc log heads");

@@ -2471,31 +2471,31 @@

 			if(am->halt)

 				ainc(&fs->rdonly);

-			qlock(&fs->mutlk);

 			for(i = 0; i < fs->narena; i++){

 				a = &fs->arenas[i];

+				oldhd[i].addr = -1;

+				oldhd[i].hash = -1;

+				oldhd[i].gen = -1;

 				qlock(a);

-				if(a->nlog < a->reserve/(10*Blksz)){

-					oldhd[i].addr = -1;

-					oldhd[i].hash = -1;

-					oldhd[i].gen = -1;

-					qunlock(a);

-					continue;

+				/*

+				 * arbitrary heuristic -- 10% of our reserved

+				 * space seems like a fine time to compress.

+				 */

+				if(a->nlog >= a->reserve/(10*Blksz)){

+					oldhd[i] = a->loghd;

+					epochstart(id);

+					if(waserror()){

+						epochend(id);

+						qunlock(a);

+						nexterror();

+					}

+					compresslog(a);

+					epochend(id);

+					poperror();

 				}

-				if(waserror()){

-					qunlock(&fs->mutlk);

-					qunlock(a);

-					nexterror();

-				}

-				oldhd[i] = a->loghd;

-				epochstart(id);

-				compresslog(a);

 				qunlock(a);

-				epochend(id);

 				epochclean();

-				poperror();

 			}

-			qunlock(&fs->mutlk);

 			sync();

 			for(i = 0; i < fs->narena; i++){

@@ -2507,8 +2507,8 @@

 					freeblk(nil, b);

 					dropblk(b);

 					epochend(id);

-					epochclean();

 					qunlock(&fs->mutlk);

+					epochclean();

 				}

 			}

@@ -2611,8 +2611,8 @@

 					epochstart(id);

 					upsert(am->mnt, mb, nm);

 					epochend(id);

-					epochclean();

 					qunlock(&fs->mutlk);

+					epochclean();

 					poperror();

 					nm = 0;

 				}