From f22ff9d05def87a049c5c8c7b86539bd4f8e3172 Mon Sep 17 00:00:00 2001 From: Fan Du Date: Tue, 30 Apr 2013 15:27:27 -0700 Subject: [PATCH] include/linux/fs.h: disable preempt when acquire i_size_seqcount write lock commit 74e3d1e17b2e11d175970b85acd44f5927000ba2 upstream. Two rt tasks bind to one CPU core. The higher priority rt task A preempts a lower priority rt task B which has already taken the write seq lock, and then the higher priority rt task A try to acquire read seq lock, it's doomed to lockup. rt task A with lower priority: call write i_size_write rt task B with higher priority: call sync, and preempt task A write_seqcount_begin(&inode->i_size_seqcount); i_size_read inode->i_size = i_size; read_seqcount_begin <-- lockup here... So disable preempt when acquiring every i_size_seqcount *write* lock will cure the problem. Signed-off-by: Fan Du Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Cc: Zhao Hongjiang Signed-off-by: Greg Kroah-Hartman --- include/linux/fs.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/fs.h b/include/linux/fs.h index 25c40b9f848a..210c347425e8 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -915,9 +915,11 @@ static inline loff_t i_size_read(const struct inode *inode) static inline void i_size_write(struct inode *inode, loff_t i_size) { #if BITS_PER_LONG==32 && defined(CONFIG_SMP) + preempt_disable(); write_seqcount_begin(&inode->i_size_seqcount); inode->i_size = i_size; write_seqcount_end(&inode->i_size_seqcount); + preempt_enable(); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT) preempt_disable(); inode->i_size = i_size;