Commit b36c92e7 authored by Petr Vandrovec's avatar Petr Vandrovec

[PATCH] Fix potential runqueue deadlock

send_sig_info() has been broken since 2.5.60.

The function can be invoked from a the time interrupt (timer_interrpt ->
do_timer -> update_process_times -> -> update_one_process -> (
do_process_times, do_it_prof, do_it_virt ) -> -> send_sig ->
send_sig_info) but it uses spin_unlock_irq instead of the correct
spin_unlock_irqrestore. 

This enables interrupts, and later scheduler_tick() locks runqueue
(without disabling interrupts).  And if we are unlucky, a new interrupt
comes at this point.  And if this interrupt tries to do wake_up() (like
RTC interrupt does), we will deadlock on runqueue lock :-(

The bug was introduced by signal-fixes-2.5.59-A4, which split the
original send_sig_info into two functions, and in one branch it started
using these unsafe spinlock variants (while the "group" variant uses
irqsave/restore correctly). 
parent 55f3c6b7
...@@ -1146,6 +1146,7 @@ int ...@@ -1146,6 +1146,7 @@ int
send_sig_info(int sig, struct siginfo *info, struct task_struct *p) send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{ {
int ret; int ret;
unsigned long flags;
/* /*
* We need the tasklist lock even for the specific * We need the tasklist lock even for the specific
...@@ -1154,9 +1155,9 @@ send_sig_info(int sig, struct siginfo *info, struct task_struct *p) ...@@ -1154,9 +1155,9 @@ send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
* going away or changing from under us. * going away or changing from under us.
*/ */
read_lock(&tasklist_lock); read_lock(&tasklist_lock);
spin_lock_irq(&p->sighand->siglock); spin_lock_irqsave(&p->sighand->siglock, flags);
ret = specific_send_sig_info(sig, info, p); ret = specific_send_sig_info(sig, info, p);
spin_unlock_irq(&p->sighand->siglock); spin_unlock_irqrestore(&p->sighand->siglock, flags);
read_unlock(&tasklist_lock); read_unlock(&tasklist_lock);
return ret; return ret;
} }
......
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