[Bug libc/24963] deadlock between freopen and fclose

["yisheng dot xys at alibaba-inc dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24963

--- Comment #8 from Yisheng Xie <yisheng.xys@alibaba-inc.com> ---
(In reply to Szabolcs Nagy from comment #6)
> lock order should be either
> 
> list_all_lock -> fp
> and then list_all_lock must not be locked while
> an fp is already locked, i.e. freopen should be
> fixed (by taking list_all_lock before the fp lock).

As list_all_lock is static variable in genops.c, do
you mean we should move it to a more common place?
Is this harder to fix?

> 
> or
> 
> fp -> list_all_lock
> and then current _IO_un_link and fflush(0) are wrong
> since they take list_all_lock first then the fp lock.
> fixing this is harder (before all _IO_un_link call fp
> should be locked and fflush should somehow lock all fps)

why cannot we let fflush follow this order too?

> 
> (i assumed both locks are recursive, if list_all_lock
> is not recursive then fixing freopen may be trickier).

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