From: Linus Torvalds <torvalds@linux-foundation.org>
To: psodagud@codeaurora.org
Cc: Kees Cook <keescook@chromium.org>,
Andy Lutomirski <luto@amacapital.net>,
Will Drewry <wad@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Eric Biggers <ebiggers@google.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
sherryy@android.com, Vegard Nossum <vegard.nossum@oracle.com>,
Christoph Lameter <cl@linux.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Sasha Levin <alexander.levin@verizon.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: write_lock_irq(&tasklist_lock)
Date: Tue, 22 May 2018 13:27:17 -0700 [thread overview]
Message-ID: <CA+55aFyGHhPvbqGaA0+tx7fbH+Uc6sbGKk2PLoFYCt-agCOgOw@mail.gmail.com> (raw)
In-Reply-To: <0879f797135033e05e8e9166a3c85628@codeaurora.org>
On Tue, May 22, 2018 at 12:40 PM Sodagudi Prasad <psodagud@codeaurora.org>
wrote:
> Have you observed this type of issues with tasklist_lock ?
tasklist_lock remains pretty painful. It covers too much, but trying to
split it up has never worked well.
It's usually not a huge problem because there are so few writers, but what
you're seeing is the writer starvation issue because readers can be
plentiful.
> Do we need write_lock_irq(&tasklist_lock) in below portion of code ? Can
> I use write_unlock instead of write_lock_irq in portion of code?
You absolutely need write_lock_irq(), because taking the tasklist_lock
without disabling interrupts will deadlock very quickly due to an interrupt
taking the tasklist_lock for reading.
That said, the write_lock_irq(&tasklist_lock) could possibly be replaced
with something like
static void tasklist_write_lock(void)
{
unsigned long flags;
local_irq_save(flags);
while (!write_trylock(&tasklist_lock)) {
local_irq_restore(flags);
do { cpu_relax(); } while (write_islocked(&tasklist_lock));
local_irq_disable();
}
}
but we don't have that "write_islocked()" function.
So the above would need more work, and is entirely untested anyway,
obviously.
Linus
next prev parent reply other threads:[~2018-05-22 20:27 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-22 19:40 write_lock_irq(&tasklist_lock) Sodagudi Prasad
2018-05-22 20:27 ` Linus Torvalds [this message]
2018-05-22 21:17 ` write_lock_irq(&tasklist_lock) Peter Zijlstra
2018-05-22 21:31 ` write_lock_irq(&tasklist_lock) Linus Torvalds
2018-05-23 8:19 ` write_lock_irq(&tasklist_lock) Peter Zijlstra
2018-05-23 13:05 ` write_lock_irq(&tasklist_lock) Will Deacon
2018-05-23 15:25 ` write_lock_irq(&tasklist_lock) Linus Torvalds
2018-05-23 15:36 ` write_lock_irq(&tasklist_lock) Will Deacon
2018-05-23 16:26 ` write_lock_irq(&tasklist_lock) Linus Torvalds
2018-05-24 12:49 ` write_lock_irq(&tasklist_lock) Will Deacon
2018-05-24 13:51 ` write_lock_irq(&tasklist_lock) Boqun Feng
2018-05-24 17:37 ` write_lock_irq(&tasklist_lock) Sodagudi Prasad
2018-05-24 18:28 ` write_lock_irq(&tasklist_lock) Peter Zijlstra
2018-05-24 21:14 ` write_lock_irq(&tasklist_lock) Andrea Parri
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