From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Andrew Morton <akpm@linux-foundation.org>,
Joel Fernandes <joel@joelfernandes.org>
Cc: "Todd Kjos" <tkjos@google.com>,
"Joel Fernandes" <joelaf@google.com>,
syzbot+a76129f18c89f3e2ddd4@syzkaller.appspotmail.com,
ak@linux.intel.com, "Johannes Weiner" <hannes@cmpxchg.org>,
jack@suse.cz, jrdr.linux@gmail.com,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, mawilcox@microsoft.com,
mgorman@techsingularity.net, syzkaller-bugs@googlegroups.com,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Martijn Coenen" <maco@android.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Subject: Re: possible deadlock in __do_page_fault
Date: Tue, 22 Jan 2019 19:02:35 +0900 [thread overview]
Message-ID: <4b0a5f8c-2be2-db38-a70d-8d497cb67665@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20180921162110.e22d09a9e281d194db3c8359@linux-foundation.org>
On 2018/09/22 8:21, Andrew Morton wrote:
> On Thu, 20 Sep 2018 19:33:15 -0400 Joel Fernandes <joel@joelfernandes.org> wrote:
>
>> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos <tkjos@google.com> wrote:
>>>
>>> +Joel Fernandes
>>>
>>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>>>>
>>>>
>>>> Thanks. Let's cc the ashmem folks.
>>>>
>>
>> This should be fixed by https://patchwork.kernel.org/patch/10572477/
>>
>> It has Neil Brown's Reviewed-by but looks like didn't yet appear in
>> anyone's tree, could Greg take this patch?
>
> All is well. That went into mainline yesterday, with a cc:stable.
>
This problem was not fixed at all.
Why do we need to call fallocate() synchronously with ashmem_mutex held?
Why can't we call fallocate() asynchronously from WQ_MEM_RECLAIM workqueue
context so that we can call fallocate() with ashmem_mutex not held?
I don't know how ashmem works, but as far as I can guess, offloading is
possible as long as other operations which depend on the completion of
fallocate() operation (e.g. read()/mmap(), querying/changing pinned status)
wait for completion of asynchronous fallocate() operation (like a draft
patch shown below is doing).
---
drivers/staging/android/ashmem.c | 50 ++++++++++++++++++++++++++++----
1 file changed, 45 insertions(+), 5 deletions(-)
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 90a8a9f1ac7d..1a890c43a10a 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -75,6 +75,17 @@ struct ashmem_range {
/* LRU list of unpinned pages, protected by ashmem_mutex */
static LIST_HEAD(ashmem_lru_list);
+static struct workqueue_struct *ashmem_wq;
+static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait);
+
+struct ashmem_shrink_work {
+ struct work_struct work;
+ struct file *file;
+ loff_t start;
+ loff_t end;
+};
+
/*
* long lru_count - The count of pages on our LRU list.
*
@@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter)
int ret = 0;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
/* If size is not set, or set to 0, always return EOF. */
if (asma->size == 0)
@@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
int ret = 0;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
/* user needs to SET_SIZE before mapping */
if (!asma->size) {
@@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
return ret;
}
+static void ashmem_shrink_worker(struct work_struct *work)
+{
+ struct ashmem_shrink_work *w = container_of(work, typeof(*w), work);
+
+ w->file->f_op->fallocate(w->file,
+ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+ w->start, w->end - w->start);
+ fput(w->file);
+ kfree(w);
+ if (atomic_dec_and_test(&ashmem_shrink_inflight))
+ wake_up_all(&ashmem_shrink_wait);
+}
+
/*
* ashmem_shrink - our cache shrinker, called from mm/vmscan.c
*
@@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
return -1;
list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
- loff_t start = range->pgstart * PAGE_SIZE;
- loff_t end = (range->pgend + 1) * PAGE_SIZE;
+ struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC);
+
+ if (!w)
+ break;
+ INIT_WORK(&w->work, ashmem_shrink_worker);
+ w->file = range->asma->file;
+ get_file(w->file);
+ w->start = range->pgstart * PAGE_SIZE;
+ w->end = (range->pgend + 1) * PAGE_SIZE;
+ atomic_inc(&ashmem_shrink_inflight);
+ queue_work(ashmem_wq, &w->work);
- range->asma->file->f_op->fallocate(range->asma->file,
- FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
- start, end - start);
range->purged = ASHMEM_WAS_PURGED;
lru_del(range);
@@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
return -EFAULT;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
if (!asma->file)
goto out_unlock;
@@ -883,8 +916,15 @@ static int __init ashmem_init(void)
goto out_free2;
}
+ ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0);
+ if (!ashmem_wq) {
+ pr_err("failed to create workqueue\n");
+ goto out_demisc;
+ }
+
ret = register_shrinker(&ashmem_shrinker);
if (ret) {
+ destroy_workqueue(ashmem_wq);
pr_err("failed to register shrinker!\n");
goto out_demisc;
}
--
2.17.1
next prev parent reply other threads:[~2019-01-22 10:02 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 21:04 possible deadlock in __do_page_fault syzbot
2018-09-20 21:10 ` Andrew Morton
2018-09-20 21:12 ` Todd Kjos
2018-09-20 23:33 ` Joel Fernandes
2018-09-21 6:37 ` Dmitry Vyukov
2018-09-21 23:21 ` Andrew Morton
2019-01-22 10:02 ` Tetsuo Handa [this message]
2019-01-22 10:12 ` Dmitry Vyukov
2019-01-22 10:32 ` Tetsuo Handa
2019-01-22 13:52 ` Dmitry Vyukov
2019-01-22 13:54 ` Dmitry Vyukov
2019-01-22 14:08 ` syzbot
2019-01-22 15:32 ` Joel Fernandes
2019-01-23 2:01 ` Tetsuo Handa
2019-01-23 15:57 ` Joel Fernandes
2019-01-24 1:52 ` Tetsuo Handa
2019-01-24 13:46 ` Joel Fernandes
2019-01-25 16:02 ` Tetsuo Handa
2019-01-28 16:45 ` Joel Fernandes
2019-01-29 10:44 ` Tetsuo Handa
2019-01-26 1:57 ` Tetsuo Handa
2018-10-01 5:23 ` syzbot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4b0a5f8c-2be2-db38-a70d-8d497cb67665@I-love.SAKURA.ne.jp \
--to=penguin-kernel@i-love.sakura.ne.jp \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=arve@android.com \
--cc=gregkh@linuxfoundation.org \
--cc=hannes@cmpxchg.org \
--cc=jack@suse.cz \
--cc=joel@joelfernandes.org \
--cc=joelaf@google.com \
--cc=jrdr.linux@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=maco@android.com \
--cc=mawilcox@microsoft.com \
--cc=mgorman@techsingularity.net \
--cc=syzbot+a76129f18c89f3e2ddd4@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tkjos@android.com \
--cc=tkjos@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).