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tty: Don't flush tty data on checkpoint stage

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In case if we're dumping the peer which another
end belongs not to us but some other application
the attempts to flush data may lead to endless
SIGTTOU storm:

 | 1158  ioctl(53, TCFLSH, 0x2)            = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
 | 1158  --- SIGTTOU {si_signo=SIGTTOU, si_code=SI_KERNEL, si_value={int=5, ptr=0x5}} ---
 | 1158  --- stopped by SIGTTOU ---
 | 1158  ioctl(53, TCFLSH, 0x2)            = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
 | 1158  --- SIGTTOU {si_signo=SIGTTOU, si_code=SI_KERNEL, si_value={int=5, ptr=0x5}} ---
 | 1158  --- stopped by SIGTTOU ---

so simply don't flush data, the initial attempt to use
TCIOFLUSH was rather "hey, we don't have a way to
say the kernel to freeze tty link for a while, lets
try to workaround this limitation" but without proper
kernel help this won't work anyway as Andrey has discovered.

Reported-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Cyrill Gorcunov 2012-11-22 19:04:12 +04:00 • committed by Pavel Emelyanov
parent 281f0c7d10
commit c19cbc5c52
1 changed files with 10 additions and 1 deletions
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11
tty.c
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@ -1158,8 +1158,17 @@ static int dump_one_pty(int lfd, u32 id, const struct fd_parms *p)
* we don't check for errors here since it makes
* no sense anyway, the buffered data is not handled
* properly yet.
*
* Note as well that if we have only one peer here
* the external end might be sending the data to us
* again and again while kernel buffer is not full,
* this might lead to endless SIGTTOU signal delivery
* to the dumpee, ruining checkpoint procedure.
*
* So simply do not flush the line while we dump
* parameters tty never was being a guaranteed delivery
* transport anyway.
*/
ioctl(lfd, TCFLSH, TCIOFLUSH);
if (!tty_test_and_set(e.tty_info_id, tty_bitmap))
ret = dump_pty_info(lfd, e.tty_info_id, p, major, index);