[lkml]   [2001]   [Jun]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [CHECKER] a couple potential deadlocks in 2.4.5-ac8
In message <> you write:
> said:
> > Good point. Spinlocks (with the exception of read-read locks, of
> > course) and semaphores will deadlock on recursive use, while the BKL
> > has this "process usage counter" recursion protection.
> Obtaining a read lock twice can deadlock too, can't it?
> A B
> read_lock()
> write_lock()
> ...sleeps...
> read_lock()
> ...sleeps...
> Or do we not make new readers sleep if there's a writer waiting?

We can never[1] make new readers sleep if there's a writer waiting, as
Linus guaranteed that an IRQ handler which only ever grabs a read lock
means the rest of the code doesn't need to block interrupts on its
read locks (see Documentation/spinlock.txt IIRC).

Also, netfilter will break (brlocks inherit this property from
their spinlocks constituents).

[1] Well, we could, but we'd have to do a special "same CPU?" check,
which would suck badly.
Premature optmztion is rt of all evl. --DK
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 12:55    [W:0.063 / U:0.460 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site