From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joseph Qi Date: Wed, 14 Sep 2016 16:25:37 +0800 Subject: [Ocfs2-devel] [PATCH] ocfs2: fix deadlock on mmapped page in ocfs2_write_begin_nolock() In-Reply-To: References: <1473501335-12519-1-git-send-email-zren@suse.com> <57D606EA.5010009@huawei.com> <5170a92c-caaf-be47-3ef8-ab9803e7a6c4@suse.com> Message-ID: <57D90981.4080504@huawei.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com Hi Eric, Sorry for the delayed response. I have got your explanation. So we have to unlock the page only in case of retry, right? If so, I think the unlock should be right before "goto try_again". Thanks, Joseph On 2016/9/14 16:04, Eric Ren wrote: > Hi Joseph, >>>> In ocfs2_write_begin_nolock(), we first grab the pages and then >>>> allocate disk space for this write; ocfs2_try_to_free_truncate_log() >>>> will be called if ENOSPC is turned; if we're lucky to get enough clusters, >>>> which is usually the case, we start over again. But in ocfs2_free_write_ctxt() >>>> the target page isn't unlocked, so we will deadlock when trying to grab >>>> the target page again. >>> IMO, in ocfs2_grab_pages_for_write, mmap_page is mapping to w_pages and >>> w_target_locked is set to true, and then will be unlocked by >>> ocfs2_unlock_pages in ocfs2_free_write_ctxt. >>> So I'm not getting the case "page isn't unlock". Could you please explain >>> it in more detail? >> Thanks for review;-) Follow up the calling chain: >> >> ocfs2_free_write_ctxt() >> ->ocfs2_unlock_pages() >> >> in ocfs2_unlock_pages (https://github.com/torvalds/linux/blob/master/fs/ocfs2/aops.c#L793), we >> can see the code just put_page(target_page), but not unlock it. > Did this answer your question? > > Thanks, > Eric >> >> Yeah, I will think this a bit more like: >> why not unlock the target_page there? Is there other potential problems if the "ret" is not "-ENOSPC" but >> other possible error code? >> >> Thanks, >> Eric >> >>> >>> Thanks, >>> Joseph >>> >>>> Fix this issue by unlocking the target page after we fail to allocate >>>> enough space at the first time. >>>> >>>> Jan Kara helps me clear out the JBD2 part, and suggest the hint for root cause. >>>> >>>> Signed-off-by: Eric Ren >>>> --- >>>> fs/ocfs2/aops.c | 7 +++++++ >>>> 1 file changed, 7 insertions(+) >>>> >>>> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c >>>> index 98d3654..78d1d67 100644 >>>> --- a/fs/ocfs2/aops.c >>>> +++ b/fs/ocfs2/aops.c >>>> @@ -1860,6 +1860,13 @@ out: >>>> */ >>>> try_free = 0; >>>> + /* >>>> + * Unlock mmap_page because the page has been locked when we >>>> + * are here. >>>> + */ >>>> + if (mmap_page) >>>> + unlock_page(mmap_page); >>>> + >>>> ret1 = ocfs2_try_to_free_truncate_log(osb, clusters_need); >>>> if (ret1 == 1) >>>> goto try_again; >>>> >>> >>> >> >> >> >> >> _______________________________________________ >> Ocfs2-devel mailing list >> Ocfs2-devel at oss.oracle.com >> https://oss.oracle.com/mailman/listinfo/ocfs2-devel > >