possible deadlock in sys_pivot_root()?
Hello,
sys_pivot_root() first takes BKL, then ->i_sem on the old root directory. On the other hand, vfs_readdir() first takes ->i_sem on a directory and then calls file system ->readdir() method, that usually takes BKL. Isn't there a deadlock possibility? Of course, sys_pivot_root() is probably not supposed to be called frequently, but still.
Nikita.
Quoted 6 lines · Nikita Danilov
Hello,
sys_pivot_root()first takes BKL, then ->i_sem on the old root directory. On the other hand,vfs_readdir()first takes ->i_sem on a directory and then calls file system ->readdir() method, that usually takes BKL. Isn't there a deadlock possibility? Of course,
Should think more before posting. Special treatment of BKL by scheduler makes this impossible.
Nikita.
Quoted 6 lines · Nikita Danilov
sys_pivot_root()first takes BKL, then ->i_sem on the old root directory. On the other hand,vfs_readdir()first takes ->i_sem on a directory and then calls file system ->readdir() method, that usually takes BKL. Isn't there a deadlock possibility? Of course,sys_pivot_root()is probably not supposed to be called frequently, but still.
No, you can't deadlock here. When you get contention on the i_sem, one thread will be put to sleep, and when that happens, the BKL will be automatically released.
So:
CPU0 CPU1
BKL
i_sem
BKL (spins, waiting for BKL to be released)
i_sem (finds it locked,
and sleeps, which
releases the BKL)
(BKL is now released, CPU1 continues)
Signature · 2 lines
Russell King ([email protected]) The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html