[PATCH] uio: fix false positive __might_sleep warning splat
From: Michal Hocko
Date: Fri Sep 04 2015 - 04:08:18 EST
Andy has reported a __might_sleep warning
[ 5174.883617] WARNING: CPU: 0 PID: 1532 at
/home/agrover/git/kernel/kernel/sched/core.c:7389 __might_sleep+0x7d/0x90()
[ 5174.884407] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffffa02a5821>] uio_read+0x91/0x170 [uio]
[ 5174.885198] Modules linked in: tcm_loop target_core_user uio target_core_pscsi target_core_file target_core_iblock iscsi_target_mod target_core_mod uinput fuse nfsv3 nfs_acl nfs lockd grace fscache sunrpc microcode i2c_piix4 virtio_balloon i2c_core xfs libcrc32c crc32c_intel virtio_net virtio_blk
[ 5174.887351] CPU: 0 PID: 1532 Comm: tcmu-runner Not tainted 4.2.0-rc7+
[ 5174.887853] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.8.1-20150318_183358- 04/01/2014
[ 5174.888633] ffffffff81a3b870 ffff880045393ca8 ffffffff817afaae
0000000000000000
[ 5174.889224] ffff880045393cf8 ffff880045393ce8 ffffffff8109a846
ffff880045393cd8
[ 5174.889793] ffffffffa02a7150 00000000000002dc 0000000000000000
ffff880045008000
[ 5174.890375] Call Trace:
[ 5174.890562] [<ffffffff817afaae>] dump_stack+0x4c/0x65
[ 5174.890938] [<ffffffff8109a846>] warn_slowpath_common+0x86/0xc0
[ 5174.891388] [<ffffffff8109a8c6>] warn_slowpath_fmt+0x46/0x50
[ 5174.891808] [<ffffffffa02a5821>] ? uio_read+0x91/0x170 [uio]
[ 5174.892237] [<ffffffffa02a5821>] ? uio_read+0x91/0x170 [uio]
[ 5174.892653] [<ffffffff810c584d>] __might_sleep+0x7d/0x90
[ 5174.893055] [<ffffffff811ea023>] __might_fault+0x43/0xa0
[ 5174.893448] [<ffffffff817b31ce>] ? schedule+0x3e/0x90
[ 5174.893820] [<ffffffffa02a58c2>] uio_read+0x132/0x170 [uio]
[ 5174.894240] [<ffffffff810cbb80>] ? wake_up_q+0x70/0x70
[ 5174.894620] [<ffffffff81236168>] __vfs_read+0x28/0xe0
[ 5174.894993] [<ffffffff81353233>] ? security_file_permission+0xa3/0xc0
[ 5174.895541] [<ffffffff8123678f>] ? rw_verify_area+0x4f/0xf0
[ 5174.896006] [<ffffffff812368ba>] vfs_read+0x8a/0x140
[ 5174.896391] [<ffffffff817b28f5>] ? __schedule+0x425/0xcc0
[ 5174.896788] [<ffffffff812375d9>] SyS_read+0x49/0xb0
The warning is a false positive because uio_read doesn't depent on
TASK_INTERRUPTIBLE after copy_to_user so it is safe to silence the
warning by an explicit setting the state to TASK_RUNNING in the path
which might call into TASK_RUNNING.
Reported-by: Andy Grover <agrover@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
drivers/uio/uio.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 3257d4220d01..7d8959e3833b 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -524,6 +524,7 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
event_count = atomic_read(&idev->event);
if (event_count != listener->event_count) {
+ __set_current_state(TASK_RUNNING);
if (copy_to_user(buf, &event_count, count))
retval = -EFAULT;
else {
--
2.5.0
--
Michal Hocko
SUSE Labs
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