Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.
Naveen N. Rao
authored
Kamalesh pointed out that we are getting the below call traces with livepatched functions when we enable CONFIG_PREEMPT: [ 495.470721] BUG: using __this_cpu_read() in preemptible [00000000] code: cat/8394 [ 495.471167] caller is is_current_kprobe_addr+0x30/0x90 [ 495.471171] CPU: 4 PID: 8394 Comm: cat Tainted: G K 4.13.0-rc7-nnr+ #95 [ 495.471173] Call Trace: [ 495.471178] [c00000008fd9b960] [c0000000009f039c] dump_stack+0xec/0x160 (unreliable) [ 495.471184] [c00000008fd9b9a0] [c00000000059169c] check_preemption_disabled+0x15c/0x170 [ 495.471187] [c00000008fd9ba30] [c000000000046460] is_current_kprobe_addr+0x30/0x90 [ 495.471191] [c00000008fd9ba60] [c00000000004e9a0] ftrace_call+0x1c/0xb8 [ 495.471195] [c00000008fd9bc30] [c000000000376fd8] seq_read+0x238/0x5c0 [ 495.471199] [c00000008fd9bcd0] [c0000000003cfd78] proc_reg_read+0x88/0xd0 [ 495.471203] [c00000008fd9bd00] [c00000000033e5d4] __vfs_read+0x44/0x1b0 [ 495.471206] [c00000008fd9bd90] [c0000000003402ec] vfs_read+0xbc/0x1b0 [ 495.471210] [c00000008fd9bde0] [c000000000342138] SyS_read+0x68/0x110 [ 495.471214] [c00000008fd9be30] [c00000000000bc6c] system_call+0x58/0x6c Commit c05b8c44 ("powerpc/kprobes: Skip livepatch_handler() for jprobes") introduced a helper is_current_kprobe_addr() to help determine if the current function has been livepatched or if it has a jprobe installed, both of which modify the NIP. This was subsequently renamed to __is_active_jprobe(). In the case of a jprobe, kprobe_ftrace_handler() disables pre-emption before calling into setjmp_pre_handler() which returns without disabling pre-emption. This is done to ensure that the jprobe handler won't disappear beneath us if the jprobe is unregistered between the setjmp_pre_handler() and the subsequent longjmp_break_handler() called from the jprobe handler. Due to this, we can use __this_cpu_read() in __is_active_jprobe() with the pre-emption check as we know that pre-emption will be disabled. However, if this function has been livepatched, we are still doing this check and when we do so, pre-emption won't necessarily be disabled. This results in the call trace shown above. Fix this by only invoking __is_active_jprobe() when pre-emption is disabled. And since we now guard this within a pre-emption check, we can instead use raw_cpu_read() to get the current_kprobe value skipping the check done by __this_cpu_read(). Fixes: c05b8c44 ("powerpc/kprobes: Skip livepatch_handler() for jprobes") Reported-by:Kamalesh Babulal <kamalesh@linux.vnet.ibm.com> Tested-by:
Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au>