From 373278a7f6678dc113b850f9ec0e09ca457cf644 Mon Sep 17 00:00:00 2001 From: Mateusz Guzik Date: Sat, 11 Jul 2020 21:57:03 +0000 Subject: [PATCH] fd: stop looping in pwd_hold We don't expect to fail acquiring the reference unless running into a corner case. Just in case ensure forward progress by taking the lock. Reviewed by: kib, markj Differential Revision: https://reviews.freebsd.org/D25616 --- sys/kern/kern_descrip.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c index 62c4d9a334cc..34e980b411ea 100644 --- a/sys/kern/kern_descrip.c +++ b/sys/kern/kern_descrip.c @@ -3347,13 +3347,17 @@ pwd_hold(struct thread *td) fdp = td->td_proc->p_fd; smr_enter(pwd_smr); - for (;;) { - pwd = smr_entered_load(&fdp->fd_pwd, pwd_smr); - MPASS(pwd != NULL); - if (refcount_acquire_if_not_zero(&pwd->pwd_refcount)) - break; + pwd = smr_entered_load(&fdp->fd_pwd, pwd_smr); + MPASS(pwd != NULL); + if (__predict_true(refcount_acquire_if_not_zero(&pwd->pwd_refcount))) { + smr_exit(pwd_smr); + return (pwd); } smr_exit(pwd_smr); + FILEDESC_SLOCK(fdp); + pwd = pwd_hold_filedesc(fdp); + MPASS(pwd != NULL); + FILEDESC_SUNLOCK(fdp); return (pwd); }