2011/1/25 Stefan Hajnoczi <stefa...@gmail.com>: > On Tue, Jan 25, 2011 at 10:13 AM, Corentin Chary > <corentin.ch...@gmail.com> wrote: >> On Tue, Jan 25, 2011 at 10:03 AM, Stefan Hajnoczi <stefa...@gmail.com> wrote: >>> On Tue, Jan 25, 2011 at 8:33 AM, Corentin Chary >>> <corentin.ch...@gmail.com> wrote: >>>> From: Yoshiaki Tamura <tamura.yoshi...@lab.ntt.co.jp> >>>> >>>> Currently qemu_set_fd_handler2() is only setting ioh->deleted upon >>>> deleting. This may cause a crash when a read handler calls >>>> qemu_set_fd_handler2() to delete handlers, but a write handler is >>>> still invoked from main_loop_wait(). Because main_loop_wait() checks >>>> handlers before calling, setting NULL upon deleting will protect >>>> handlers being called if already deleted. >>>> >>>> One example is the new threaded vnc server. When an error occurs in >>>> the context of a read handler, it'll releases resources and deletes >>>> handlers. However, because the write handler still exists, it'll be >>>> called, and then crashes because of lack of resources. This patch >>>> fixes it. >>> >>> Does this case still happen with qemu.git/master? In November I sent >>> a patch to check for deleted handlers: >>> >>> commit 0290b57bdfec83ca78b6d119ea9847bb17943328 >>> Author: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> >>> Date: Wed Nov 3 14:29:44 2010 +0000 >>> >>> Delete IOHandlers after potentially running them >>> >>> Since commit 4bed9837309e58d208183f81d8344996744292cf an .fd_read() >>> handler that deletes its IOHandler is exposed to .fd_write() being >>> called on the deleted IOHandler. >>> >>> This patch fixes deletion so that .fd_read() and .fd_write() are never >>> called on an IOHandler that is marked for deletion. >>> >>> Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> >>> Signed-off-by: Anthony Liguori <aligu...@us.ibm.com> >>> >>> So I don't think Yoshi's patch is necessary anymore? >> >> Ho I didn't see that one. >> It's probably not necessary, but it stills make sense to apply this >> patch since there is >> absolutly no reasons to keep the old value in fd_read and fd_write when >> the user explicitly asked to set them to NULL. > > That's true, I don't see a good reason why we shouldn't clear them. > The only minor advantage to keeping them is that it helps when > debugging QEMU - you can identify the fd handler by its > fd_read/fd_write function pointers easily.
Well, since I posted the patch in August, I won't get surprised even the bug might be fixed due to other patches :) Regardless of that, I don't see the patch is doing something incorrect either. If some codes were relying on unset values, that should be wrong. Yoshi > > Stefan > >
