Messages in this thread Patch in this message | | | From | Fan Du <> | Subject | [PATCH] Disable preempt when acquire i_size_seqcount write lock | Date | Fri, 21 Dec 2012 16:41:13 +0800 |
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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 <fan.du@windriver.com> --- 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
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