Message ID | 20200508130633.2532759-1-mpe@ellerman.id.au (mailing list archive) |
---|---|
State | Accepted |
Commit | 38b407be172d3d15afdbfe172691b7caad98120f |
Headers | show |
Series | [v2] powerpc/spufs: Rework fcheck() usage | expand |
Context | Check | Description |
---|---|---|
snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (1bc92fe3175eb26ff37e580c0383d7a9abe06835) |
snowpatch_ozlabs/build-ppc64le | success | Build succeeded |
snowpatch_ozlabs/build-ppc64be | success | Build succeeded |
snowpatch_ozlabs/build-ppc64e | success | Build succeeded |
snowpatch_ozlabs/build-pmac32 | success | Build succeeded |
snowpatch_ozlabs/checkpatch | warning | total: 0 errors, 1 warnings, 0 checks, 46 lines checked |
snowpatch_ozlabs/needsstable | success | Patch has no Fixes tags |
On Fri, 8 May 2020 23:06:33 +1000, Michael Ellerman wrote: > Currently the spu coredump code triggers an RCU warning: > > ============================= > WARNING: suspicious RCU usage > 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Not tainted > ----------------------------- > include/linux/fdtable.h:95 suspicious rcu_dereference_check() usage! > > [...] Applied to powerpc/next. [1/1] powerpc/spufs: Rework fcheck() usage https://git.kernel.org/powerpc/c/38b407be172d3d15afdbfe172691b7caad98120f cheers
diff --git a/arch/powerpc/platforms/cell/spufs/coredump.c b/arch/powerpc/platforms/cell/spufs/coredump.c index 8b3296b62f65..37c155254cd5 100644 --- a/arch/powerpc/platforms/cell/spufs/coredump.c +++ b/arch/powerpc/platforms/cell/spufs/coredump.c @@ -82,13 +82,20 @@ static int match_context(const void *v, struct file *file, unsigned fd) */ static struct spu_context *coredump_next_context(int *fd) { + struct spu_context *ctx; struct file *file; int n = iterate_fd(current->files, *fd, match_context, NULL); if (!n) return NULL; *fd = n - 1; + + rcu_read_lock(); file = fcheck(*fd); - return SPUFS_I(file_inode(file))->i_ctx; + ctx = SPUFS_I(file_inode(file))->i_ctx; + get_spu_context(ctx); + rcu_read_unlock(); + + return ctx; } int spufs_coredump_extra_notes_size(void) @@ -99,17 +106,23 @@ int spufs_coredump_extra_notes_size(void) fd = 0; while ((ctx = coredump_next_context(&fd)) != NULL) { rc = spu_acquire_saved(ctx); - if (rc) + if (rc) { + put_spu_context(ctx); break; + } + rc = spufs_ctx_note_size(ctx, fd); spu_release_saved(ctx); - if (rc < 0) + if (rc < 0) { + put_spu_context(ctx); break; + } size += rc; /* start searching the next fd next time */ fd++; + put_spu_context(ctx); } return size;
Currently the spu coredump code triggers an RCU warning: ============================= WARNING: suspicious RCU usage 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Not tainted ----------------------------- include/linux/fdtable.h:95 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by spu-coredump/1343: #0: c0000007fa22f430 (sb_writers#2){.+.+}-{0:0}, at: .do_coredump+0x1010/0x13c8 stack backtrace: CPU: 0 PID: 1343 Comm: spu-coredump Not tainted 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Call Trace: .dump_stack+0xec/0x15c (unreliable) .lockdep_rcu_suspicious+0x120/0x144 .coredump_next_context+0x148/0x158 .spufs_coredump_extra_notes_size+0x54/0x190 .elf_coredump_extra_notes_size+0x34/0x50 .elf_core_dump+0xe48/0x19d0 .do_coredump+0xe50/0x13c8 .get_signal+0x864/0xd88 .do_notify_resume+0x158/0x3c8 .interrupt_exit_user_prepare+0x19c/0x208 interrupt_return+0x14/0x1c0 This comes from fcheck_files() via fcheck(). It's pretty clearly documented that fcheck() must be wrapped with rcu_read_lock(), adding that fixes the RCU warning. hch points out that once we've released the RCU read lock the file may be closed and freed, which would leave us with a pointer to a freed spu_context. To avoid that, take a reference to the spu_context while we hold the RCU read lock, and drop that reference later once we're done with the context. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> --- arch/powerpc/platforms/cell/spufs/coredump.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) v2: Take a reference and hold it until we're done.