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Subject: [PATCH v2 2/6] proc: use down_read_killable mmap_sem for
 /proc/pid/smaps_rollup
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Michal =?utf-8?q?Koutn=C3=BD?= <mkoutny@suse.com>,
        Al Viro <viro@zeniv.linux.org.uk>, Roman Gushchin <guro@fb.com>
Date:   Sun, 09 Jun 2019 13:08:54 +0300
Message-ID: <156007493429.3335.14666825072272692455.stgit@buzz>
In-Reply-To: <156007465229.3335.10259979070641486905.stgit@buzz>
References: <156007465229.3335.10259979070641486905.stgit@buzz>
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Do not stuck forever if something wrong.
Killable lock allows to cleanup stuck tasks and simplifies investigation.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 fs/proc/task_mmu.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2bf210229daf..781879a91e3b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -832,7 +832,10 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
 	memset(&mss, 0, sizeof(mss));
 
-	down_read(&mm->mmap_sem);
+	ret = down_read_killable(&mm->mmap_sem);
+	if (ret)
+		goto out_put_mm;
+
 	hold_task_mempolicy(priv);
 
 	for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
@@ -849,8 +852,9 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
 	release_task_mempolicy(priv);
 	up_read(&mm->mmap_sem);
-	mmput(mm);
 
+out_put_mm:
+	mmput(mm);
 out_put_task:
 	put_task_struct(priv->task);
 	priv->task = NULL;