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Generation numbers to catch write back of stale copies

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Oops when a stale copy is written back, i.e. the processor was yielded
since the copy was made.  Such bugs are difficult to spot.  Sequence
numbers catch them when they do actual harm (they also catch different
bugs).  Generation numbers catch them even when they don't.

New ef_generation to count generations.  Call new ef_make_stale() to
increment it whenever the processor may be yielded.

New struct emptypedstr member generation.  To conserve space, make it
a bit-field of twelve bits, i.e. generations are only recorded modulo
2^12.  Make sure all members of unit empobj_storage share it.  It is
only used in copies; its value on disk and in the cache is
meaningless.  Copies with generation other than ef_generation are
stale.  Stale copies that are a multiple of 2^12 generations old can't
be detected, but that is sufficiently improbable.

Set generation to ef_generation by calling new ef_mark_fresh() when
making copies in ef_read() and ef_blank().  nav_ship() and
fltp_to_list() make copies without going through ef_read(), and
therefore need to call ef_mark_fresh() as well.  Also call it in
obj_changed() to make check_sect_ok() & friends freshen their argument
when it is unchanged.

New must_be_fresh() oopses when its argument is stale.  Call it in
ef_write() to catch write back of stale copies.
This commit is contained in:
Markus Armbruster 2009-12-31 13:14:36 +01:00
parent 358aee203e
commit 2fa5f65257
22 changed files with 93 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

40
src/lib/common/file.c
View file

@ -57,9 +57,12 @@ static int do_read(struct empfile *, void *, int, int);
static int do_write(struct empfile *, void *, int, int);
static unsigned get_seqno(struct empfile *, int);
static void new_seqno(struct empfile *, void *);
static void must_be_fresh(struct empfile *, void *);
static void do_blank(struct empfile *, void *, int, int);
static int ef_check(int);
static unsigned ef_generation;
/*
* Open the file-backed table TYPE (EF_SECTOR, ...).
* HOW are flags to control operation. Naturally, immutable flags are
@ -360,6 +363,7 @@ ef_read(int type, int id, void *into)
cachep = ep->cache + (id - ep->baseid) * ep->size;
}
memcpy(into, cachep, ep->size);
ef_mark_fresh(type, into);
if (ep->postread)
ep->postread(id, into);
@ -522,9 +526,11 @@ ef_write(int type, int id, void *from)
if (ep->onresize && ep->onresize(type) < 0)
return 0;
}
if (id >= ep->baseid && id < ep->baseid + ep->cids)
if (id >= ep->baseid && id < ep->baseid + ep->cids) {
cachep = ep->cache + (id - ep->baseid) * ep->size;
else
if (cachep != from)
must_be_fresh(ep, from);
} else
cachep = NULL;
if (ep->prewrite)
ep->prewrite(id, cachep, from);
@ -607,6 +613,35 @@ new_seqno(struct empfile *ep, void *buf)
elt->seqno = old_seqno + 1;
}
void
ef_make_stale(void)
{
ef_generation++;
}
void
ef_mark_fresh(int type, void *buf)
{
struct empfile *ep;
if (ef_check(type) < 0)
return;
ep = &empfile[type];
if (!(ep->flags & EFF_TYPED))
return;
((struct emptypedstr *)buf)->generation = ef_generation;
}
static void
must_be_fresh(struct empfile *ep, void *buf)
{
struct emptypedstr *elt = buf;
if (!(ep->flags & EFF_TYPED))
return;
CANT_HAPPEN(elt->generation != (ef_generation & 0xfff));
}
/*
* Extend table TYPE by COUNT elements.
* Any pointers obtained from ef_ptr() become invalid.
@ -684,6 +719,7 @@ ef_blank(int type, int id, void *buf)
elt = buf;
elt->seqno = get_seqno(ep, elt->uid);
}
ef_mark_fresh(type, buf);
}
/*