| From | Luis Henriques <> | Subject | [PATCH 3.5 74/78] include/linux/fs.h: disable preempt when acquire i_size_seqcount write lock | Date | Mon, 25 Nov 2013 13:07:01 +0000 |
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3.5.7.26 -stable review patch. If anyone has any objections, please let me know.
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From: Fan Du <fan.du@windriver.com>
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 <fan.du@windriver.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Zhao Hongjiang <zhaohongjiang@huawei.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- include/linux/fs.h | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/include/linux/fs.h b/include/linux/fs.h index 17fd887..65b8b69 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -925,9 +925,11 @@ 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; -- 1.8.3.2
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