Author: kib Date: Fri Nov 13 09:31:57 2020 New Revision: 367631 URL: https://svnweb.freebsd.org/changeset/base/367631
Log: Implement vn_lock_pair(). In collaboration with: pho Reviewed by: mckusick (previous version), markj (previous version) Tested by: markj (syzkaller), pho Sponsored by: The FreeBSD Foundation Differential revision: https://reviews.freebsd.org/D26136 Modified: head/sys/kern/vfs_vnops.c head/sys/sys/vnode.h Modified: head/sys/kern/vfs_vnops.c ============================================================================== --- head/sys/kern/vfs_vnops.c Fri Nov 13 02:05:45 2020 (r367630) +++ head/sys/kern/vfs_vnops.c Fri Nov 13 09:31:57 2020 (r367631) @@ -70,6 +70,7 @@ __FBSDID("$FreeBSD$"); #include <sys/filio.h> #include <sys/resourcevar.h> #include <sys/rwlock.h> +#include <sys/prng.h> #include <sys/sx.h> #include <sys/sleepqueue.h> #include <sys/sysctl.h> @@ -275,6 +276,10 @@ restart: vn_finished_write(mp); if (error) { NDFREE(ndp, NDF_ONLY_PNBUF); + if (error == ERELOOKUP) { + NDREINIT(ndp); + goto restart; + } return (error); } fmode &= ~O_TRUNC; @@ -1524,6 +1529,7 @@ vn_truncate(struct file *fp, off_t length, struct ucre vp = fp->f_vnode; +retry: /* * Lock the whole range for truncation. Otherwise split i/o * might happen partly before and partly after the truncation. @@ -1550,6 +1556,8 @@ out: vn_finished_write(mp); out1: vn_rangelock_unlock(vp, rl_cookie); + if (error == ERELOOKUP) + goto retry; return (error); } @@ -3317,4 +3325,92 @@ vn_fallocate(struct file *fp, off_t offset, off_t len, } return (error); +} + +static u_long vn_lock_pair_pause_cnt; +SYSCTL_ULONG(_debug, OID_AUTO, vn_lock_pair_pause, CTLFLAG_RD, + &vn_lock_pair_pause_cnt, 0, + "Count of vn_lock_pair deadlocks"); + +static void +vn_lock_pair_pause(const char *wmesg) +{ + atomic_add_long(&vn_lock_pair_pause_cnt, 1); + pause(wmesg, prng32_bounded(hz / 10)); +} + +/* + * Lock pair of vnodes vp1, vp2, avoiding lock order reversal. + * vp1_locked indicates whether vp1 is exclusively locked; if not, vp1 + * must be unlocked. Same for vp2 and vp2_locked. One of the vnodes + * can be NULL. + * + * The function returns with both vnodes exclusively locked, and + * guarantees that it does not create lock order reversal with other + * threads during its execution. Both vnodes could be unlocked + * temporary (and reclaimed). + */ +void +vn_lock_pair(struct vnode *vp1, bool vp1_locked, struct vnode *vp2, + bool vp2_locked) +{ + int error; + + if (vp1 == NULL && vp2 == NULL) + return; + if (vp1 != NULL) { + if (vp1_locked) + ASSERT_VOP_ELOCKED(vp1, "vp1"); + else + ASSERT_VOP_UNLOCKED(vp1, "vp1"); + } else { + vp1_locked = true; + } + if (vp2 != NULL) { + if (vp2_locked) + ASSERT_VOP_ELOCKED(vp2, "vp2"); + else + ASSERT_VOP_UNLOCKED(vp2, "vp2"); + } else { + vp2_locked = true; + } + if (!vp1_locked && !vp2_locked) { + vn_lock(vp1, LK_EXCLUSIVE | LK_RETRY); + vp1_locked = true; + } + + for (;;) { + if (vp1_locked && vp2_locked) + break; + if (vp1_locked && vp2 != NULL) { + if (vp1 != NULL) { + error = VOP_LOCK1(vp2, LK_EXCLUSIVE | LK_NOWAIT, + __FILE__, __LINE__); + if (error == 0) + break; + VOP_UNLOCK(vp1); + vp1_locked = false; + vn_lock_pair_pause("vlp1"); + } + vn_lock(vp2, LK_EXCLUSIVE | LK_RETRY); + vp2_locked = true; + } + if (vp2_locked && vp1 != NULL) { + if (vp2 != NULL) { + error = VOP_LOCK1(vp1, LK_EXCLUSIVE | LK_NOWAIT, + __FILE__, __LINE__); + if (error == 0) + break; + VOP_UNLOCK(vp2); + vp2_locked = false; + vn_lock_pair_pause("vlp2"); + } + vn_lock(vp1, LK_EXCLUSIVE | LK_RETRY); + vp1_locked = true; + } + } + if (vp1 != NULL) + ASSERT_VOP_ELOCKED(vp1, "vp1 ret"); + if (vp2 != NULL) + ASSERT_VOP_ELOCKED(vp2, "vp2 ret"); } Modified: head/sys/sys/vnode.h ============================================================================== --- head/sys/sys/vnode.h Fri Nov 13 02:05:45 2020 (r367630) +++ head/sys/sys/vnode.h Fri Nov 13 09:31:57 2020 (r367631) @@ -729,6 +729,8 @@ bool vn_isdisk_error(struct vnode *vp, int *errp); bool vn_isdisk(struct vnode *vp); int _vn_lock(struct vnode *vp, int flags, const char *file, int line); #define vn_lock(vp, flags) _vn_lock(vp, flags, __FILE__, __LINE__) +void vn_lock_pair(struct vnode *vp1, bool vp1_locked, struct vnode *vp2, + bool vp2_locked); int vn_open(struct nameidata *ndp, int *flagp, int cmode, struct file *fp); int vn_open_cred(struct nameidata *ndp, int *flagp, int cmode, u_int vn_open_flags, struct ucred *cred, struct file *fp); _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
