From de95c84d3e86af34b5d3268c80e8f5b779620c76 Mon Sep 17 00:00:00 2001 From: David van Moolenbroek Date: Wed, 16 Sep 2015 10:41:46 +0000 Subject: [PATCH] VFS: fix short select(2) timeouts Some select queries require a response from device drivers. If a select call is nonblocking (with a zero timeout), the response to the caller may have to be deferred until all involved drivers have responded to the initial query. This is handled just fine. However, if the select call has a timeout that is so short that it triggers before all the involved drivers have responded, the resulting alarm would be discarded, possibly resulting in the call blocking forever. This fix changes the alarm handler such that if the alarm triggers too early, the select call is further handled as though it was nonblocking. This fix resolves a test77 deadlock on really slow systems. Change-Id: Ib487c8fe436802c3e11c57355ae0c8480721f06e --- minix/servers/vfs/select.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/minix/servers/vfs/select.c b/minix/servers/vfs/select.c index 5bf2a1171..c042698ff 100644 --- a/minix/servers/vfs/select.c +++ b/minix/servers/vfs/select.c @@ -755,8 +755,10 @@ void select_timeout_check(minix_timer_t *timer) if (se->requestor == NULL) return; if (se->expiry <= 0) return; /* Strange, did we even ask for a timeout? */ se->expiry = 0; - if (is_deferred(se)) return; /* Wait for initial replies to CDEV_SELECT */ - select_return(se); + if (!is_deferred(se)) + select_return(se); + else + se->block = 0; /* timer triggered "too soon", treat as nonblocking */ }