be6577af0c
Stalls are quite frequent with recent kernels. I enabled CONFIG_SOFTLOCKUP_DETECTOR and I caught the following stall: watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [cc1:22803] CPU: 0 PID: 22803 Comm: cc1 Not tainted 5.6.17+ #3 Hardware name: 9000/800/rp3440 IAOQ[0]: d_alloc_parallel+0x384/0x688 IAOQ[1]: d_alloc_parallel+0x388/0x688 RP(r2): d_alloc_parallel+0x134/0x688 Backtrace: [<000000004036974c>] __lookup_slow+0xa4/0x200 [<0000000040369fc8>] walk_component+0x288/0x458 [<000000004036a9a0>] path_lookupat+0x88/0x198 [<000000004036e748>] filename_lookup+0xa0/0x168 [<000000004036e95c>] user_path_at_empty+0x64/0x80 [<000000004035d93c>] vfs_statx+0x104/0x158 [<000000004035dfcc>] __do_sys_lstat64+0x44/0x80 [<000000004035e5a0>] sys_lstat64+0x20/0x38 [<0000000040180054>] syscall_exit+0x0/0x14 The code was stuck in this loop in d_alloc_parallel: 4037d414: 0e 00 10 dc ldd 0(r16),ret0 4037d418: c7 fc 5f ed bb,< ret0,1f,4037d414 <d_alloc_parallel+0x384> 4037d41c: 08 00 02 40 nop This is the inner loop of bit_spin_lock which is called by hlist_bl_unlock in d_alloc_parallel: static inline void bit_spin_lock(int bitnum, unsigned long *addr) { /* * Assuming the lock is uncontended, this never enters * the body of the outer loop. If it is contended, then * within the inner loop a non-atomic test is used to * busywait with less bus contention for a good time to * attempt to acquire the lock bit. */ preempt_disable(); #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) while (unlikely(test_and_set_bit_lock(bitnum, addr))) { preempt_enable(); do { cpu_relax(); } while (test_bit(bitnum, addr)); preempt_disable(); } #endif __acquire(bitlock); } After consideration, I realized that we must be losing bit unlocks. Then, I noticed that we missed defining atomic64_set_release(). Adding this define fixes the stalls in bit operations. Signed-off-by: Dave Anglin <dave.anglin@bell.net> Cc: stable@vger.kernel.org Signed-off-by: Helge Deller <deller@gmx.de> |
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.