Author: mjg Date: Thu Nov 19 19:25:47 2020 New Revision: 367852 URL: https://svnweb.freebsd.org/changeset/base/367852
Log: pipe: thundering herd problem in pipelock All reads and writes are serialized with a hand-rolled lock, but unlocking it always wakes up all waiters. Existing flag fields get resized to make room for introduction of waiter counter without growing the struct. Reviewed by: kib Differential Revision: https://reviews.freebsd.org/D27273 Modified: head/sys/kern/sys_pipe.c head/sys/sys/pipe.h Modified: head/sys/kern/sys_pipe.c ============================================================================== --- head/sys/kern/sys_pipe.c Thu Nov 19 19:05:16 2020 (r367851) +++ head/sys/kern/sys_pipe.c Thu Nov 19 19:25:47 2020 (r367852) @@ -622,9 +622,13 @@ pipelock(struct pipe *cpipe, int catch) if (catch) prio |= PCATCH; while (cpipe->pipe_state & PIPE_LOCKFL) { - cpipe->pipe_state |= PIPE_LWANT; + KASSERT(cpipe->pipe_waiters >= 0, + ("%s: bad waiter count %d", __func__, + cpipe->pipe_waiters)); + cpipe->pipe_waiters++; error = msleep(cpipe, PIPE_MTX(cpipe), prio, "pipelk", 0); + cpipe->pipe_waiters--; if (error != 0) return (error); } @@ -642,10 +646,12 @@ pipeunlock(struct pipe *cpipe) PIPE_LOCK_ASSERT(cpipe, MA_OWNED); KASSERT(cpipe->pipe_state & PIPE_LOCKFL, ("Unlocked pipe passed to pipeunlock")); + KASSERT(cpipe->pipe_waiters >= 0, + ("%s: bad waiter count %d", __func__, + cpipe->pipe_waiters)); cpipe->pipe_state &= ~PIPE_LOCKFL; - if (cpipe->pipe_state & PIPE_LWANT) { - cpipe->pipe_state &= ~PIPE_LWANT; - wakeup(cpipe); + if (cpipe->pipe_waiters > 0) { + wakeup_one(cpipe); } } Modified: head/sys/sys/pipe.h ============================================================================== --- head/sys/sys/pipe.h Thu Nov 19 19:05:16 2020 (r367851) +++ head/sys/sys/pipe.h Thu Nov 19 19:25:47 2020 (r367852) @@ -116,9 +116,10 @@ struct pipe { struct pipe *pipe_peer; /* link with other direction */ struct pipepair *pipe_pair; /* container structure pointer */ u_short pipe_state; /* pipe status info */ - u_short pipe_type; /* pipe type info */ + u_char pipe_type; /* pipe type info */ + u_char pipe_present; /* still present? */ + int pipe_waiters; /* pipelock waiters */ int pipe_busy; /* busy flag, mostly to handle rundown sanely */ - int pipe_present; /* still present? */ int pipe_wgen; /* writer generation for named pipe */ ino_t pipe_ino; /* fake inode for stat(2) */ }; _______________________________________________ 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"
