On Thu, Apr 13, 2017 at 4:50 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > On Thu, 2017-04-13 at 16:13 -0400, Anna Schumaker wrote: >> >> On 04/13/2017 03:16 PM, Anna Schumaker wrote: >> > >> > >> > On 04/13/2017 03:07 PM, Olga Kornievskaia wrote: >> > > On Thu, Apr 13, 2017 at 2:51 PM, Trond Myklebust >> > > <trondmy@xxxxxxxxxxxxxxx> wrote: >> > > > On Thu, 2017-04-13 at 14:00 -0400, Olga Kornievskaia wrote: >> > > > > Hi folks, >> > > > > >> > > > > Looking for suggestions on how to fix a kernel oops. >> > > > > >> > > > > It's possible that there is a ctrl-c when the COMMIT is send. >> > > > > In case >> > > > > of the COPY, it calls >> > > > > nfs_commit_file() which calls wait_on_commit() that is >> > > > > interrupted by >> > > > > the crtl-c and frees the nfs_page request. So when >> > > > > asynchronous >> > > > > COMMIT >> > > > > rpc comes back it tried to use the nfs_page request and gets >> > > > > the >> > > > > oops. >> > > > > >> > > > >> > > > Is that call to nfs_free_request() in nfs_commit_file() >> > > > correct? >> > > >> > > yes, nfs_commit_file() creates a new request via >> > > nfs_create_request() >> > > and in the end if calls nfs_free_request(); >> > > >> > > > It looks to me as if the same request will be freed in >> > > > nfs_commit_release_pages(). >> > > >> > > so nfs_commit_release_pages() thru the >> > > nfs_unlock_and_release_request() is going to call >> > > nfs_release_request() from req->wb_kref.. I'm not sure if this is >> > > setup(?) for the copy commit path? >> > > >> > > Otherwise, it would have seem that we'd be doing a double free >> > > and I >> > > haven't seen that in testing (not that it can't be true)... >> > >> > I haven't seen any double-free messages during my testing either, >> > so I thought it was okay. It's possible I'm wrong, though. I >> > wonder if this is something that memory poisoning can help figure >> > out? >> >> After some experimenting, I can still use the nfs_page after >> nfs_commit_inode() has returned withotu any memory issues. >> > > Wait... > > OK, so nfs_scan_commit_list() does indeed take a reference to the req- >>wb_kref, so that balances the call to nfs_release_request() in > nfs_commit_release_pages(), however it also means that you should not > be calling nfs_free_request(), since doing so circumvents the > refcounting mechanism. > Right now when req is created in nfs_commit_file() it starts out with wb_kref=1. After calling, nfs_scan_commit_list() wb_kref=2 Now if in normal operations nfs_commit_release_pages will drop that to 1 And then calling nfs_release_commit in nfs_commit_file() will finally drop to 0 and release. If ctrl-c happened, then nfs_commit_file will drop the ref first but will not free it and that will allow the commit to proceed and finish the rpc? > Secondly, if you want to release the request and you are not sure > whether or not it got cleared off the inode's cinfo commit list yet, > you may also need to lock that request and call > nfs_clear_request_commit(). Looking at what the function does, I don't see why this is needed. "wb_page" is NULL for this type of commit and there is no pnfs in this case. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
