Messages in this thread | | | Date | Sun, 8 Mar 2015 01:33:20 +0000 | From | Al Viro <> | Subject | Re: [RFC] ->poll() bugs |
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On Sat, Mar 07, 2015 at 12:53:14PM -0800, Linus Torvalds wrote: > On Sat, Mar 7, 2015 at 12:44 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > Most of the catch consists of ->poll() instances that return -E...; there's > > also an unpleasant mess in net/9p/trans_fd.c and a braino in sunrpc > > unexpectedly caught by the same annotations. > > Hmm. I do wonder if we should just *allow* ->poll() to return an > error, and just turn it into "all bits set"?
Doable, but... we do have a bunch of ->poll() call sites (AFAICS, right now it's drivers/staging/comedi/drivers/serial2002.c:142: drivers/vfio/pci/vfio_pci_intrs.c:191: drivers/vhost/vhost.c:95: fs/eventpoll.c:800: fs/proc/inode.c:229: fs/select.c:461: fs/select.c:764: mm/memcontrol.c:4285: net/9p/trans_fd.c:249: net/9p/trans_fd.c:254: virt/kvm/eventfd.c:418: ) and while they could be turned into calls of a wrapper, I really don't like returning negatives as a part of ->poll() calling conventions. I mean, really - "you should return a bitmap of POLL... flags *or* -E...; doesn't matter which error number it is, it'll be lost anyway"... It's OK to have the caller(s) catch such bugs (and report them, IMO), but silently treating it that way as a part of calling conventions...
Besides, that doesn't catch the bugs like one in net/9p; sparse annotations do.
> But if getting sparse to catch them all isn't *too* painful and the > patch doesn't end up being horribly big, then I guess that's ok.
Getting sparse to catch them all is as trivial as * introduce a __bitwise typedef __poll_t => unsigned int * say that ->poll() (in file_operations, as well as in proto_ops, tty_ldisc_ops and several in other subsystems) returns __poll_t * switch the return type of instances from unsigned int to __poll_t * do the same to local variable(s) (if any) used to hold the return value to be.
Again, from cc(1) POV it's a no-op - unannotated foo_poll() will be just fine as it is. The only place where I did something more fancy than such type change actually had been buggy - drivers/media/common/siano/smsdvb-debugfs.c:smsdvb_stats_poll() relied upon smsdvb_stats_wait_read() never returning negatives and it needs s/__poll_t rc/& = 0/ for correctness (fixed and folded).
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