linux-kernel - [PATCH 4.19 091/113] proc: use down_read_killable mmap_sem for /proc/pid/clear

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Date:   Mon, 29 Jul 2019 21:22:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Roman Gushchin <guro@...com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michal Hocko <mhocko@...e.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Koutný <mkoutny@...e.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 091/113] proc: use down_read_killable mmap_sem for /proc/pid/clear_refs

[ Upstream commit c46038017fbdcac627b670c9d4176f1d0c2f5fa3 ]

Do not remain stuck forever if something goes wrong.  Using a killable
lock permits cleanup of stuck tasks and simplifies investigation.

Replace the only unkillable mmap_sem lock in clear_refs_write().

Link: http://lkml.kernel.org/r/156007493826.3335.5424884725467456239.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Reviewed-by: Roman Gushchin <guro@...com>
Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>
Reviewed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Michal Koutný <mkoutny@...e.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/proc/task_mmu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 74965e17ffd5..195fbbaf77d4 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1131,7 +1131,10 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 			goto out_mm;
 		}
 
-		down_read(&mm->mmap_sem);
+		if (down_read_killable(&mm->mmap_sem)) {
+			count = -EINTR;
+			goto out_mm;
+		}
 		tlb_gather_mmu(&tlb, mm, 0, -1);
 		if (type == CLEAR_REFS_SOFT_DIRTY) {
 			for (vma = mm->mmap; vma; vma = vma->vm_next) {
-- 
2.20.1