path: root/Documentation
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authorDavid Rientjes <rientjes@google.com>2014-06-23 13:22:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-23 16:47:43 -0700
commit7cd2b0a34ab8e4db971920eef8982f985441adfb (patch)
tree0c8732b3ff3712bbad8b58696ad98c6f7fb17c05 /Documentation
parentdf2e1ef68c51ddccfdb6f34f92ee9f93541de802 (diff)
mm, pcp: allow restoring percpu_pagelist_fraction default
Oleg reports a division by zero error on zero-length write() to the percpu_pagelist_fraction sysctl: divide error: 0000 [#1] SMP DEBUG_PAGEALLOC CPU: 1 PID: 9142 Comm: badarea_io Not tainted 3.15.0-rc2-vm-nfs+ #19 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff8800d5aeb6e0 ti: ffff8800d87a2000 task.ti: ffff8800d87a2000 RIP: 0010: percpu_pagelist_fraction_sysctl_handler+0x84/0x120 RSP: 0018:ffff8800d87a3e78 EFLAGS: 00010246 RAX: 0000000000000f89 RBX: ffff88011f7fd000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000010 RBP: ffff8800d87a3e98 R08: ffffffff81d002c8 R09: ffff8800d87a3f50 R10: 000000000000000b R11: 0000000000000246 R12: 0000000000000060 R13: ffffffff81c3c3e0 R14: ffffffff81cfddf8 R15: ffff8801193b0800 FS: 00007f614f1e9740(0000) GS:ffff88011f440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00007f614f1fa000 CR3: 00000000d9291000 CR4: 00000000000006e0 Call Trace: proc_sys_call_handler+0xb3/0xc0 proc_sys_write+0x14/0x20 vfs_write+0xba/0x1e0 SyS_write+0x46/0xb0 tracesys+0xe1/0xe6 However, if the percpu_pagelist_fraction sysctl is set by the user, it is also impossible to restore it to the kernel default since the user cannot write 0 to the sysctl. This patch allows the user to write 0 to restore the default behavior. It still requires a fraction equal to or larger than 8, however, as stated by the documentation for sanity. If a value in the range [1, 7] is written, the sysctl will return EINVAL. This successfully solves the divide by zero issue at the same time. Signed-off-by: David Rientjes <rientjes@google.com> Reported-by: Oleg Drokin <green@linuxhacker.ru> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index bd4b34c03738..4415aa915681 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -702,7 +702,8 @@ The batch value of each per cpu pagelist is also updated as a result. It is
set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
The initial value is zero. Kernel does not use this value at boot time to set
-the high water marks for each per cpu page list.
+the high water marks for each per cpu page list. If the user writes '0' to this
+sysctl, it will revert to this default behavior.

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