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ocfs2: Avoid livelock in ocfs2_readpage() 

When someone writes to an inode, readers accessing the same inode via
ocfs2_readpage() just busyloop trying to get ip_alloc_sem because
do_generic_file_read() looks up the page again and retries ->readpage()
when previous attempt failed with AOP_TRUNCATED_PAGE. When there are enough
readers, they can occupy all CPUs and in non-preempt kernel the system is
deadlocked because writer holding ip_alloc_sem is never run to release the
semaphore. Fix the problem by making reader block on ip_alloc_sem to break
the busy loop.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Joel Becker <jlbec@evilplan.org>
This commit is contained in:
Jan Kara 2011-06-23 22:51:47 +02:00 committed by Joel Becker
parent a11f7e63c5
commit c7e25e6e0b
1 changed files with 8 additions and 0 deletions
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8
fs/ocfs2/aops.c
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@ -290,7 +290,15 @@ static int ocfs2_readpage(struct file *file, struct page *page)
}
if (down_read_trylock(&oi->ip_alloc_sem) == 0) {
/*
* Unlock the page and cycle ip_alloc_sem so that we don't
* busyloop waiting for ip_alloc_sem to unlock
*/
ret = AOP_TRUNCATED_PAGE;
unlock_page(page);
unlock = 0;
down_read(&oi->ip_alloc_sem);
up_read(&oi->ip_alloc_sem);
goto out_inode_unlock;
}