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xenbus: fix deadlock on writes to /proc/xen/xenbus 

/proc/xen/xenbus does not work correctly.  A read blocked waiting for
a xenstore message holds the mutex needed for atomic file position
updates.  This blocks any writes on the same file handle, which can
deadlock if the write is needed to unblock the read.

Clear FMODE_ATOMIC_POS when opening this device to always get
character device like sematics.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
David Vrabel 2016-12-09 14:41:13 +00:00 committed by Juergen Gross
parent 3da96be58f
commit 581d21a2d0
1 changed files with 2 additions and 0 deletions
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2
drivers/xen/xenbus/xenbus_dev_frontend.c
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@ -538,6 +538,8 @@ static int xenbus_file_open(struct inode *inode, struct file *filp)
nonseekable_open(inode, filp);
filp->f_mode &= ~FMODE_ATOMIC_POS; /* cdev-style semantics */
u = kzalloc(sizeof(*u), GFP_KERNEL);
if (u == NULL)
return -ENOMEM;