The patch titled
Subject: include/linux/fs.h: disable preempt when acquire i_size_seqcount write lock
has been added to the -mm tree. Its filename is
include-linux-fsh-disable-preempt-when-acquire-i_size_seqcount-write-lock.patch
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------------------------------------------------------
From: Fan Du <fan.du@xxxxxxxxxxxxx>
Subject: include/linux/fs.h: disable preempt when acquire i_size_seqcount write lock
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@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/fs.h | 2 ++
1 file changed, 2 insertions(+)
diff -puN include/linux/fs.h~include-linux-fsh-disable-preempt-when-acquire-i_size_seqcount-write-lock include/linux/fs.h
--- a/include/linux/fs.h~include-linux-fsh-disable-preempt-when-acquire-i_size_seqcount-write-lock
+++ a/include/linux/fs.h
@@ -675,9 +675,11 @@ static inline loff_t i_size_read(const s
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;
_
Patches currently in -mm which might be from fan.du@xxxxxxxxxxxxx are
include-linux-fsh-disable-preempt-when-acquire-i_size_seqcount-write-lock.patch
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