On Donnerstag, 16. Juni 2022 15:51:31 CEST Dominique Martinet wrote:
Christian Schoenebeck wrote on Thu, Jun 16, 2022 at 03:35:59PM +0200:
- I fixed the conflict and gave your patch a test spin, and it triggers
the BUG_ON(!fid); that you added with that patch. Backtrace based on
30306f6194ca ("Merge tag 'hardening-v5.19-rc3' ..."):
hm, that's probably the version I sent without the fallback to private_data fid if writeback fid was sent (I've only commented without sending a v2)
Right, I forgot that you queued another version, sorry. With your already queued patch (today's v2) that's fine now.
On Donnerstag, 16. Juni 2022 16:11:16 CEST Dominique Martinet wrote:
Dominique Martinet wrote on Thu, Jun 16, 2022 at 10:51:31PM +0900:
Did your patch work there for you? I mean I have not applied the other pending 9p patches, but they should not really make difference, right? I won't have time today, but I will continue to look at it tomorrow. If you already had some thoughts on this, that would be great of course.
Yes, my version passes basic tests at least, and I could no longer reproduce the problem.
For what it's worth I've also tested a version of your patch:
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c index a8f512b44a85..d0833fa69faf 100644 --- a/fs/9p/vfs_addr.c +++ b/fs/9p/vfs_addr.c @@ -58,8 +58,21 @@ static void v9fs_issue_read(struct netfs_io_subrequest *subreq) */ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file) {
struct inode *inode = file_inode(file);
struct v9fs_inode *v9inode = V9FS_I(inode); struct p9_fid *fid = file->private_data;
BUG_ON(!fid);
/* we might need to read from a fid that was opened write-only
* for read-modify-write of page cache, use the writeback fid* for that */if (rreq->origin == NETFS_READ_FOR_WRITE &&
(fid->mode & O_ACCMODE) == O_WRONLY) {fid = v9inode->writeback_fid;BUG_ON(!fid);}
refcount_inc(&fid->count); rreq->netfs_priv = fid; return 0;
And this also seems to work alright.
I was about to ask why the original code did writes with the writeback fid, but I'm noticing now the current code still does (through v9fs_vfs_write_folio_locked()), so that part hasn't changed from the old code, and init_request will only be getting reads? Which actually makes sense now I'm thinking about it because I recall David saying he's working on netfs writes now...
So that minimal version is probably what we want, give or take style adjustments (only initializing inode/v9inode in the if case or not) -- I sure hope compilers optimizes it away when not needed.
I'll let you test one or both versions and will fixup the commit message again/credit you/resend if we go with this version, unless you want to send it.
-- Dominique
I tested all 3 variants today, and they were all behaving correctly (no EBADF errors anymore, no other side effects observed).
The minimalistic version (i.e. your initial suggestion) performed 20% slower in my tests, but that could be due to the fact that it was simply the 1st version I tested, so caching on host side might be the reason. If necessary I can check the performance aspect more thoroughly.
Personally I would at least use the NETFS_READ_FOR_WRITE version, but that's up to you. On doubt, clarify with David's plans.
Feel free to add my RB and TB tags to any of the 3 version(s) you end up queuing:
Reviewed-by: Christian Schoenebeck linux_oss@crudebyte.com Tested-by: Christian Schoenebeck linux_oss@crudebyte.com
Best regards, Christian Schoenebeck