Date: Thu, 7 Oct 2004 19:49:39 GMT From: Mark Gooderum <mark@verniernetworks.com> To: freebsd-gnats-submit@FreeBSD.org Subject: threads/72429: threads blocked in stdio (fgets, etc) are not cancellable in 5.3 (works in 4.x) Message-ID: <200410071949.i97Jndpw004041@www.freebsd.org> Resent-Message-ID: <200410071950.i97JoR03079645@freefall.freebsd.org>
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>Number: 72429
>Category: threads
>Synopsis: threads blocked in stdio (fgets, etc) are not cancellable in 5.3 (works in 4.x)
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: freebsd-threads
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Thu Oct 07 19:50:27 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator: Mark Gooderum
>Release: 5.3 Beta 6
>Organization:
Vernier Networks, Inc.
>Environment:
FreeBSD 172.20.1.199 5.3-BETA6 FreeBSD 5.3-BETA6 #0: Thu Oct 7 09:35:49 PDT 2004 root@eagle.jumpadmin.net:/usr/build/ambit2/freebsd5/sys/i386/compile/VNISMP i386
>Description:
With libc_r in 4.9 a function blocked in stdio (say fgets()) is cancellable. The call from fgets() to the I/O in FreeBSD 4.9 with libc/libc_r:
fgets()
__srefill()
__sread() (via fp->_read())
_read() (now in libc_r)
calls thread_enter_cancellation_point()
calls __read()
__read() does the uthread I/O voodoo
thread can be cancelled...
With FreeBSD 5.3 libc/libpthread:
fgets()
__srefill()
__sread() (via fp->_read())
_read() - weak symbol for __sys_read() in libc
(libpthread only defines __read and a weak reference from read
to __read)
thread can't be cancelled - it's blocked in real system call
and thread_enter_cancellation_point() was never called
With FreeBSD 5.3 libc/libpthread:
fgets()
__srefill()
__sread() (via fp->_read())
_read() (now in libc_r)
_read() does the uthread I/O voodoo
thread can't be cancelled as
thread_enter_cancellation_point() was never called, that
is in __read()...
>How-To-Repeat:
Try to pthread_cancel() a thread blocked in any stdio operation (fgets, fread, etc), it will never cancel.
>Fix:
Given the current conventions for _foo, __foo and foo it seems like __sread et. al. should be calling the foo() versions of the functions so they get wrapped as cancellation points.
>Release-Note:
>Audit-Trail:
>Unformatted:
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