shithub: gefs

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fs: fix race between walk and remove

we need a double check that the file is in the tree
because the walk to the fid is done in a reader proc
that can look it up in a stale version of the tree,
while we clunk the dent in the mutator proc.

--- a/fs.c

+++ b/fs.c

@@ -1668,9 +1668,11 @@

 static void

 fsremove(Fmsg *m, int id, Amsg **ao)

 {

-	char *e, upbuf[Upksz];

+	char *e, buf[Kvmax];

 	Fcall r;

 	Msg mb[2];

+	Tree *t;

+	Kvp kv;

 	Fid *f;

 	if((f = getfid(m->conn, m->fid)) == nil){

@@ -1677,6 +1679,7 @@

 		rerror(m, Enofid);

 		return;

 	}

+	t = f->mnt->root;

 	clunkfid(m->conn, f);

 	truncwait(f->dent, id);

@@ -1690,6 +1693,17 @@

 	}

 	if(f->dent->gone)

 		error(Ephase);

+	/*

+	 * we need a double check that the file is in the tree

+	 * here, because the walk to the fid is done in a reader

+	 * proc that can look it up in a stale version of the

+	 * tree, while we clunk the dent in the mutator proc.

+	 *

+	 * this means we can theoretically get some deletions

+	 * of files that are already gone.

+	 */

+	if(!btlookup(t, &f->dent->Key, &kv, buf, sizeof(buf)))

+		error(Ephase);

 	if((e = candelete(f)) != nil)

 		error(e);

 	if(fsaccess(f, f->dmode, f->duid, f->dgid, DMWRITE) == -1)

@@ -1700,9 +1714,9 @@

 	mb[0].nv = 0;

 	if(f->dent->qid.type & QTDIR){

-		packsuper(upbuf, sizeof(upbuf), f->qpath);

+		packsuper(buf, sizeof(buf), f->qpath);

 		mb[1].op = Oclobber;

-		mb[1].k = upbuf;

+		mb[1].k = buf;

 		mb[1].nk = Upksz;

 		mb[1].nv = 0;

 		upsert(f->mnt, mb, 2);