From f2e70d8f2fdff0707b3f4de4ef87f93e4396320c Mon Sep 17 00:00:00 2001 From: Bob Peterson Date: Wed, 6 Oct 2021 09:29:18 -0500 Subject: gfs2: fix GL_SKIP node_scope problems Before this patch, when a glock was locked, the very first holder on the queue would unlock the lockref and call the go_instantiate glops function (if one existed), unless GL_SKIP was specified. When we introduced the new node-scope concept, we allowed multiple holders to lock glocks in EX mode and share the lock. But node-scope introduced a new problem: if the first holder has GL_SKIP and the next one does NOT, since it is not the first holder on the queue, the go_instantiate op was not called. Eventually the GL_SKIP holder may call the instantiate sub-function (e.g. gfs2_rgrp_bh_get) but there was still a window of time in which another non-GL_SKIP holder assumes the instantiate function had been called by the first holder. In the case of rgrp glocks, this led to a NULL pointer dereference on the buffer_heads. This patch tries to fix the problem by introducing two new glock flags: GLF_INSTANTIATE_NEEDED, which keeps track of when the instantiate function needs to be called to "fill in" or "read in" the object before it is referenced. GLF_INSTANTIATE_IN_PROG which is used to determine when a process is in the process of reading in the object. Whenever a function needs to reference the object, it checks the GLF_INSTANTIATE_NEEDED flag, and if set, it sets GLF_INSTANTIATE_IN_PROG and calls the glops "go_instantiate" function. As before, the gl_lockref spin_lock is unlocked during the IO operation, which may take a relatively long amount of time to complete. While unlocked, if another process determines go_instantiate is still needed, it sees GLF_INSTANTIATE_IN_PROG is set, and waits for the go_instantiate glop operation to be completed. Once GLF_INSTANTIATE_IN_PROG is cleared, it needs to check GLF_INSTANTIATE_NEEDED again because the other process's go_instantiate operation may not have been successful. Functions that previously called the instantiate sub-functions now call directly into gfs2_instantiate so the new bits are managed properly. Signed-off-by: Bob Peterson Signed-off-by: Andreas Gruenbacher --- fs/gfs2/glock.h | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/gfs2/glock.h') diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h index a36104229d0d..4f8642301801 100644 --- a/fs/gfs2/glock.h +++ b/fs/gfs2/glock.h @@ -204,6 +204,7 @@ extern void gfs2_holder_reinit(unsigned int state, u16 flags, extern void gfs2_holder_uninit(struct gfs2_holder *gh); extern int gfs2_glock_nq(struct gfs2_holder *gh); extern int gfs2_glock_poll(struct gfs2_holder *gh); +extern int gfs2_instantiate(struct gfs2_holder *gh); extern int gfs2_glock_wait(struct gfs2_holder *gh); extern int gfs2_glock_async_wait(unsigned int num_gh, struct gfs2_holder *ghs); extern void gfs2_glock_dq(struct gfs2_holder *gh); -- cgit v1.2.3