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| author |   Anton Ivanov <aivanov@brocade.com> | 2015-12-21 11:28:02 +0000 |
|---|---|---|
| committer |   Richard Weinberger <richard@nod.at> | 2016-01-10 21:49:47 +0100 |
| commit | d5e3f5cbe5cee7fe6da26566559a978547179b37 (patch) | |
| tree | 7f40e2da3a070e811a412865ffbf5c317844e257 /arch/um | |
| parent | uml: flush stdout before forking (diff) | |
| download | linux-dev-d5e3f5cbe5cee7fe6da26566559a978547179b37.tar.xz linux-dev-d5e3f5cbe5cee7fe6da26566559a978547179b37.zip | |
um: Prevent IRQ handler reentrancy
The existing IRQ handler design in UML does not prevent reentrancy
This is mitigated by fd-enable/fd-disable semantics for the IO
portion of the UML subsystem. The timer, however, can and is
re-entered resulting in very deep stack usage and occasional
stack exhaustion.
This patch prevents this by checking if there is a timer
interrupt in-flight before processing any pending timer interrupts.
Signed-off-by: Anton Ivanov <aivanov@brocade.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Diffstat (limited to 'arch/um')
| -rw-r--r-- | arch/um/os-Linux/signal.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c index c211153ca69a..7801666514ed 100644 --- a/arch/um/os-Linux/signal.c +++ b/arch/um/os-Linux/signal.c @@ -62,6 +62,7 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) static int signals_enabled; static unsigned int signals_pending; +static unsigned int signals_active = 0; void sig_handler(int sig, struct siginfo *si, mcontext_t *mc) { @@ -101,7 +102,12 @@ void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc) block_signals(); + signals_active |= SIGALRM_MASK; + timer_real_alarm_handler(mc); + + signals_active &= ~SIGALRM_MASK; + set_signals(enabled); } @@ -286,8 +292,16 @@ void unblock_signals(void) if (save_pending & SIGIO_MASK) sig_handler_common(SIGIO, NULL, NULL); - if (save_pending & SIGALRM_MASK) + /* Do not reenter the handler */ + + if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK))) timer_real_alarm_handler(NULL); + + /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */ + + if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK)) + return; + } } |