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Currently the fragment info is placed at the top of the linked list

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under a shared read lock. This patch attempts to upgrade the lock to
an exclusive write lock. If the exclusive write lock fails to be
obtained, the current fragment is not placed at the head of the list.

This portion of the patch was inspired by NetBSD ip_frag.c r1.4 (which
effectively removed the section of code that performed the reordering).

The patch to sys/contrib/ipfilter/netinet/ip_compat.h adds the
MUTEX_TRY_UPGRADE macro to support the patch to ip_frag.c.

The patch to contrib/ipfilter/lib/rwlock_emul.c supports this patch
by emulating the mutex in userspace when exercised by ipftest(1).

Inspired by:	NetBSD ip_frag.c r1.4
MFC after:	1 month
This commit is contained in:
Cy Schubert 2017-01-26 01:24:05 +00:00
parent cbf1505df9
commit 971fa117c0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=312787
3 changed files with 27 additions and 1 deletions
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21
contrib/ipfilter/lib/rwlock_emul.c
View File

@ -56,6 +56,27 @@ void eMrwlock_write_enter(rw, file, line)
}
void eMrwlock_try_upgrade(rw, file, line)
eMrwlock_t *rw;
char *file;
int line;
{
if (rw->eMrw_magic != EMM_MAGIC) {
fprintf(stderr, "%s:eMrwlock_write_enter(%p): bad magic: %#x\n",
rw->eMrw_owner, rw, rw->eMrw_magic);
abort();
}
if (rw->eMrw_read != 0 || rw->eMrw_write != 0) {
fprintf(stderr,
"%s:eMrwlock_try_upgrade(%p): already locked: %d/%d\n",
rw->eMrw_owner, rw, rw->eMrw_read, rw->eMrw_write);
abort();
}
rw->eMrw_write++;
rw->eMrw_heldin = file;
rw->eMrw_heldat = line;
}
void eMrwlock_downgrade(rw, file, line)
eMrwlock_t *rw;
char *file;

4
sys/contrib/ipfilter/netinet/ip_compat.h
View File

@ -165,6 +165,7 @@ struct ether_addr {
# define READ_ENTER(x) rw_rlock(&(x)->ipf_lk)
# define WRITE_ENTER(x) rw_wlock(&(x)->ipf_lk)
# define MUTEX_DOWNGRADE(x) rw_downgrade(&(x)->ipf_lk)
# define MUTEX_TRY_UPGRADE(x) rw_try_upgrade(&(x)->ipf_lk)
# define RWLOCK_INIT(x,y) rw_init(&(x)->ipf_lk, (y))
# define RW_DESTROY(x) rw_destroy(&(x)->ipf_lk)
# define RWLOCK_EXIT(x) do { \
@ -421,6 +422,8 @@ extern void freembt __P((mb_t *));
# define MUTEX_DOWNGRADE(x) eMrwlock_downgrade(&(x)->ipf_emu, \
__FILE__, __LINE__)
# define MUTEX_TRY_UPGRADE(x) eMrwlock_try_upgrade(&(x)->ipf_emu, \
__FILE__, __LINE__)
# define READ_ENTER(x) eMrwlock_read_enter(&(x)->ipf_emu, \
__FILE__, __LINE__)
# define RWLOCK_INIT(x, y) eMrwlock_init(&(x)->ipf_emu, y)
@ -671,6 +674,7 @@ extern char *ipf_getifname __P((struct ifnet *, char *));
# define READ_ENTER(x) ;
# define WRITE_ENTER(x) ;
# define MUTEX_DOWNGRADE(x) ;
# define MUTEX_TRY_UPGRADE(x) ;
# define RWLOCK_INIT(x, y) ;
# define RWLOCK_EXIT(x) ;
# define RW_DESTROY(x) ;

3
sys/contrib/ipfilter/netinet/ip_frag.c
View File

@ -745,7 +745,7 @@ ipf_frag_lookup(softc, softf, fin, table
} else if (off == 0)
f->ipfr_seen0 = 1;
if (f != table[idx]) {
if (f != table[idx] && MUTEX_TRY_UPGRADE(lock)) {
ipfr_t **fp;
/*
@ -763,6 +763,7 @@ ipf_frag_lookup(softc, softf, fin, table
table[idx]->ipfr_hprev = &f->ipfr_hnext;
f->ipfr_hprev = table + idx;
table[idx] = f;
MUTEX_DOWNGRADE(lock);
}
/*