From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fan Du Subject: [PATCH] fs: Disable preempt when acquire i_size_seqcount write lock Date: Wed, 9 Jan 2013 11:34:19 +0800 Message-ID: <1357702459-2718-1-git-send-email-fan.du@windriver.com> Mime-Version: 1.0 Content-Type: text/plain Cc: , , To: Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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 --- include/linux/fs.h | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index db84f77..1b69e87 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -758,9 +758,11 @@ 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; -- 1.7.0.5